:books: To learn more about DevOps and SRE, check the resources in [devops-resources](https://github.com/bregman-arie/devops-resources) repository
:warning: You can use these for preparing for an interview but most of the questions and exercises don't represent an actual interview. Please read [Q&A](common-qa.md) for more details
:busts_in_silhouette: [Join](https://www.facebook.com/groups/538897960007080) our [DevOps community](https://www.facebook.com/groups/538897960007080) where we have discussions and share resources on DevOps
"DevOps is the combination of cultural philosophies, practices, and tools that increases an organization’s ability to deliver applications and services at high velocity: evolving and improving products at a faster pace than organizations using traditional software development and infrastructure management processes. This speed enables organizations to better serve their customers and compete more effectively in the market."
"DevOps is the union of people, process, and products to enable continuous delivery of value to our end users. The contraction of “Dev” and “Ops” refers to replacing siloed Development and Operations to create multidisciplinary teams that now work together with shared and efficient practices and tools. Essential DevOps practices include agile planning, continuous integration, continuous delivery, and monitoring of applications."
Red Hat:
"DevOps describes approaches to speeding up the processes by which an idea (like a new software feature, a request for enhancement, or a bug fix) goes from development to deployment in a production environment where it can provide value to the user. These approaches require that development teams and operations teams communicate frequently and approach their work with empathy for their teammates. Scalability and flexible provisioning are also necessary. With DevOps, those that need power the most, get it—through self service and automation. Developers, usually coding in a standard development environment, work closely with IT operations to speed software builds, tests, and releases—without sacrificing reliability."
"...The organizational and cultural movement that aims to increase software delivery velocity, improve service reliability, and build shared ownership among software stakeholders"
* One person is in charge of specific tasks. For example there is only one person who is allowed to merge the code of everyone else into the repository.
* Configuration Management - Ansible, Puppet, Chef
* Monitoring & alerting - Prometheus, Nagios
* Logging - Logstash, Graylog, Fluentd
* Code review - Gerrit, Review Board
* Code coverage - Cobertura, Clover, JaCoCo
* Issue tracking - Jira, Bugzilla
* Containers and Containers Orchestration - Docker, Podman, Kubernetes, Nomad
* Tests - Robot, Serenity, Gauge
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<summary>A team member of yours, suggests to replace the current CI/CD platform used by the organization with a new one. How would you reply?</summary><br><b>
Things to think about:
* What we gain from doing so? Are there new features in the new platform? Does the new platform deals with some of the limitations presented in the current platform?
* What this suggestion is based on? In other words, did he/she tried out the new platform? Was there extensive technical research?
* What does the switch from one platform to another will require from the organization? For example, training users who use the platform? How much time the team has to invest in such move?
* Version control is the sytem of tracking and managing changes to software code.
* It helps software teams to manage changes to source code over time.
* Version control also helps developers move faster and allows software teams to preserve efficiency and agility as the team scales to include more developers.
* Merging is Git's way of putting a forked history back together again. The git merge command lets you take the independent lines of development created by git branch and integrate them into a single branch.
* A merge conflict is an event that occurs when Git is unable to automatically resolve differences in code between two commits. When all the changes in the code occur on different lines or in different files, Git will successfully merge commits without your help.
A development practice where developers integrate code into a shared repository frequently. It can range from a couple of changes every day or a week to a couple of changes in one hour in larger scales.
Each piece of code (change/patch) is verified, to make the change is safe to merge. Today, it's a common practice to test the change using an automated build that makes sure the code can integrated. It can be one build which runs several tests in different levels (unit, functional, etc.) or several separate builds that all or some has to pass in order for the change to be merged into the repository.
<summary>What is Continuous Deployment?</summary><br><b>
A development strategy used by developers to release software automatically into production where any code commit must pass through an automated testing phase. Only when this is successful is the release considered production worthy. This eliminates any human interaction and should be implemented only after production-ready pipelines have been set with real-time monitoring and reporting of deployed assets. If any issues are detected in production it should be easy to rollback to previous working state.
For more info please read [here](https://www.atlassian.com/continuous-delivery/continuous-deployment)
<summary>Can you describe an example of a CI (and/or CD) process starting the moment a developer submitted a change/PR to a repository?</summary><br><b>
There are many answers for such a question, as CI processes vary, depending on the technologies used and the type of the project to where the change was submitted.
A developer submitted a pull request to a project. The PR (pull request) triggered two jobs (or one combined job). One job for running lint test on the change and the second job for building a package which includes the submitted change, and running multiple api/scenario tests using that package. Once all tests passed and the change was approved by a maintainer/core, it's merged/pushed to the repository. If some of the tests failed, the change will not be allowed to merged/pushed to the repository.
A complete different answer or CI process, can describe how a developer pushes code to a repository, a workflow then triggered to build a container image and push it to the registry. Once in the registry, the k8s cluster is applied with the new changes.
A development strategy used to frequently deliver code to QA and Ops for testing. This entails having a staging area that has production like features where changes can only be accepted for production after a manual review. Because of this human entanglement there is usually a time lag between release and review making it slower and error prone as compared to continous deployment.
For more info please read [here](https://www.atlassian.com/continuous-delivery/continuous-deployment)
* Testing/Staging environment should be a clone of production environment.
* Clean up your environments (e.g. your CI/CD pipelines may create a lot of resources. They should also take care of cleaning up everything they create)
* The CI/CD pipelines should provide the same results when executed locally or remotely
* Treat CI/CD as another application in your organization. Not as a glue code.
* On demand environments instead of pre-allocated resources for CI/CD purposes
* Stages/Steps/Tasks of pipelines should be shared between applications or microservices (don't re-invent common tasks like "cloning a project")
<summary>You are given a pipeline and a pool with 3 workers: virtual machine, baremetal and a container. How will you decide on which one of them to run the pipeline?</summary><br><b>
1. App Repository - store them in the same repository of the application they are building or testing (perhaps the most popular one)
2. Central Repository - store all organization's/project's CI/CD pipelines in one separate repository (perhaps the best approach when multiple teams test the same set of projects and they end up having many pipelines)
3. CI repo for every app repo - you separate CI related code from app code but you don't put everything in one place (perhaps the worst option due to the maintenance)
<summary>Would you prefer a "configuration->deployment" model or "deployment->configuration"? Why?</summary><br><b>
Both have advantages and disadvantages.
With "configuration->deployment" model for example, where you build one image to be used by multiple deployments, there is less chance of deployments being different from one another, so it has a clear advantage of a consistent environment.
Read [this](https://venam.nixers.net/blog/unix/2020/03/29/distro-pkgs.html) fantastic article on the topic.
From the article: "Thus, software distribution is about the mechanism and the community that takes the burden and decisions to build an assemblage of coherent software that can be shipped."
Different distributions can focus on different things like: focus on different environments (server vs. mobile vs. desktop), support specific hardware, specialize in different domains (security, multimedia, ...), etc. Basically, different aspects of the software and what it supports, get different priority in each distribution.
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<summary>What is a Software Repository?</summary><br><b>
Wikipedia: "A software repository, or “repo” for short, is a storage location for software packages. Often a table of contents is stored, as well as metadata."
Read more [here](https://en.wikipedia.org/wiki/Software_repository)
* Source - Maintain build script within version control system so that user can build your app after cloning repository. Advantage: User can quickly checkout different versions of application. Disadvantage: requires build tools installed on users machine.
* Archive - collect all your app files into one archive (e.g. tar) and deliver it to the user. Advantage: User gets everything he needs in one file. Disadvantage: Requires repeating the same procedure when updating, not good if there are a lot of dependencies.
* Package - depends on the OS, you can use your OS package format (e.g. in RHEL/Fefodra it's RPM) to deliver your software with a way to install, uninstall and update it using the standard packager commands. Advantages: Package manager takes care of support for installation, uninstallation, updating and dependency management. Disadvantage: Requires managing package repository.
* Images - Either VM or container images where your package is included with everything it needs in order to run successfully. Advantage: everything is preinstalled, it has high degree of environment isolation. Disadvantage: Requires knowledge of building and optimizing images.
Caching is fast access to frequently used resources which are computationally expensive or IO intensive and do not change often. There can be several layers of cache that can start from CPU caches to distributed cache systems. Common ones are in memory caching and distributed caching. <br/> Caches are typically data structures that contains some data, such as a hashtable or dictionary. However, any data structure can provide caching capabilities, like set, sorted set, sorted dictionary etc. While, caching is used in many applications, they can create subtle bugs if not implemented correctly or used correctly. For example,cache invalidation, expiration or updating is usually quite challenging and hard.
<summary>What is Reliability? How does it fit DevOps?</summary><br><b>
Reliability, when used in DevOps context, is the ability of a system to recover from infrastructure failure or disruption. Part of it is also being able to scale based on your organization or team demands.
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<summary>What "Availability" means? What means are there to track Availability of a service?</summary><br><b>
<summary>You need to install periodically a package (unless it's already exists) on different operating systems (Ubuntu, RHEL, ...). How would you do it?</summary><br><b>
Wikipedia: "Chaos engineering is the discipline of experimenting on a software system in production in order to build confidence in the system's capability to withstand turbulent and unexpected conditions"
IAC (infrastructure as code) is a declerative approach of defining infrastructure or architecture of a system. Some implementations are ARM templates for Azure and Terraform that can work across multiple cloud providers.
Build artifacts are usually stored in a repository. They can be used in release pipelines for deployment purposes. Usually there is retention period on the build artifacts.
<summary>You joined a team where everyone developing one project and the practice is to run tests locally on their workstation and push it to the repository if the tests passed. What is the problem with the process as it is now and how to improve it?</summary><br><b>
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<summary>Explain test-driven development (TDD)</summary><br><b>
Configuration drift can be avoided with desired state configuration (DSC) implementation. Desired state configuration can be a declarative file that defined how a system should be. There are tools to enforce desired state such a terraform or azure dsc. There are incramental or complete strategies.
<summary>Explain Declarative and Procedural styles. The technologies you are familiar with (or using) are using procedural or declarative style?</summary><br><b>
To better emphasize the difference, consider creating two virtual instances/servers.
In declarative style, you would specify two servers and the tool will figure out how to reach that state.
In procedural style, you need to specify the steps to reach the end state of two instances/servers - for example, create a loop and in each iteration of the loop create one instance (running the loop twice of course).
Note: cross-dependency is when you have two or more changes to separate projects and you would like to test them in mutual build instead of testing each change separately.
GitLab: "GitOps is an operational framework that takes DevOps best practices used for application development such as version control, collaboration, compliance, and CI/CD tooling, and applies them to infrastructure automation".
Read more [here](https://about.gitlab.com/topics/gitops)
Google: "One could view DevOps as a generalization of several core SRE principles to a wider range of organizations, management structures, and personnel."
Read more about it [here](https://sre.google/sre-book/introduction)
Google: "the SRE team is responsible for availability, latency, performance, efficiency, change management, monitoring, emergency response, and capacity planning of their services"
Jenkins is an open source automation tool written in Java with plugins built for Continuous Integration purpose. Jenkins is used to build and test your software projects continuously making it easier for developers to integrate changes to the project, and making it easier for users to obtain a fresh build. It also allows you to continuously deliver your software by integrating with a large number of testing and deployment technologies.
Jenkins integrates development life-cycle processes of all kinds, including build, document, test, package, stage, deploy, static analysis and much more.
- Job is an automation definition = what and where to execute once the user clicks on "build"
- Build is a running instance of a job. You can have one or more builds at any given point of time (unless limited by confiugration)
- A worker is the machine/instance on which the build is running. When a build starts, it "acquires" a worker out of a pool to run on it.
- An executor is variable of the worker, defining how many builds can run on that worker in parallel. An executor value of 3 means, that 3 builds can run at any point on that executor (not necessarily of the same job. Any builds)
<summary>You need to run unit tests every time a change submitted to a given project. Describe in details how your pipeline would look like and what will be executed in each stage</summary><br><b>
You can describe the UI way to add new nodes but better to explain how to do in a way that scales like a script or using dynamic source for nodes like one of the existing clouds.
<summary>Whenever a build fails, you would like to notify the team owning the job regarding the failure and provide failure reason. How would you do that?</summary><br><b>
<summary>There are four teams in your organization. How to prioritize the builds of each team? So the jobs of team x will always run before team y for example</summary><br><b>
<summary>If you are managing a dozen of jobs, you can probably use the Jenkins UI. But how do you manage the creation and deletion of hundreds of jobs every week/month?</summary><br><b>
Cloud computing refers to the delivery of on-demand computing services
over the internet on a pay-as-you-go basis.
In simple words, Cloud computing is a service that lets you use any computing
service such as a server, storage, networking, databases, and intelligence,
right through your browser without owning anything. You can do anything you
can think of unless it doesn’t require you to stay close to your hardware.
Cloud service providers are companies that establish public clouds, manage private clouds, or offer on-demand cloud computing components (also known as cloud computing services) like Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS), and Software-as-a-Service(SaaS). Cloud services can reduce business process costs when compared to on-premise IT.
* Pay as you go (or consumption-based payment) - you are paying only for what you are using. No upfront payments and payment stops when resources are no longer used.
* Scalable - resources are scaled down or up based on demand
* IAAS - Users have control over complete Operating System and don't need to worry about the physical resources, which is managed by Cloud Service Provider.
* PAAS - CLoud Service Provider takes care of Operating System, Middlewares and users only need to focus on our Data and Application.
* SAAS - A cloud based method to provide software to users, software logics running on cloud, can be run on-premises or managed by Cloud Service Provider.
In cloud providers, someone else owns and manages the hardware, hire the relevant infrastructure teams and pays for real-estate (for both hardware and people). You can focus on your business.
In On-Premise solution, it's quite the opposite. You need to take care of hardware, infrastructure teams and pay for everything which can be quite expensive. On the other hand it's tailored to your needs.
The main idea behind serverless computing is that you don't need to manage the creation and configuration of server. All you need to focus on is splitting your app into multiple functions which will be triggered by some actions.
It's important to note that:
* Serverless Computing is still using servers. So saying there are no servers in serverless computing is completely wrong
* Serverless Computing allows you to have a different paying model. You basically pay only when your functions are running and not when the VM or containers are running as in other payment models
AWS definition: "AWS Auto Scaling monitors your applications and automatically adjusts capacity to maintain steady, predictable performance at the lowest possible cost"
Read more about auto scaling [here](https://aws.amazon.com/autoscaling)
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<summary>True or False? Auto Scaling is about adding resources (such as instances) and not about removing resource</summary><br><b>
False. Auto scaling adjusts capacity and this can mean removing some resources based on usage and performances.
Within each region, there are multiple isolated locations known as Availability Zones. Multiple availability zones ensure high availability in case one of them goes down.<br>
Edge locations are basically content delivery network which caches data and insures lower latency and faster delivery to the users in any location. They are located in major cities in the world.
<summary>A user is unable to access an s3 bucket. What might be the problem?</summary><br><b>
There can be several reasons for that. One of them is lack of policy. To solve that, the admin has to attach the user with a policy what allows him to access the s3 bucket.
Amazon definition: "Amazon Elastic Container Service (Amazon ECS) is a fully managed container orchestration service. Customers such as Duolingo, Samsung, GE, and Cook Pad use ECS to run their most sensitive and mission critical applications because of its security, reliability, and scalability."
Learn more [here](https://aws.amazon.com/ecs)
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<summary>What is Amazon ECR?</summary><br><b>
Amazon definition: "Amazon Elastic Container Registry (ECR) is a fully-managed Docker container registry that makes it easy for developers to store, manage, and deploy Docker container images."
Amazon definition: "AWS Fargate is a serverless compute engine for containers that works with both Amazon Elastic Container Service (ECS) and Amazon Elastic Kubernetes Service (EKS)."
S3 is a object storage service which is fast, scalable and durable. S3 enables customers to upload, download or store any file or object that is up to 5 TB in size.
* Long-lived data with changing or unknown access patterns. Basically, In this class the data automatically moves to the class most suitable for you based on usage patterns
* Price depends on the used class
* 11x9% durability
* 99.90% availability
* Glacier: Archive data with retrieval time ranging from minutes to hours
* Glacier Deep Archive: Archive data that rarely, if ever, needs to be accessed with retrieval times in hours
* Both Glacier and Glacier Deep Archive are:
* The most cheap storage classes
* have 9x9% durability
More on storage classes [here](https://aws.amazon.com/s3/storage-classes)
<summary>A customer would like to move data which is rarely accessed from standard storage class to the most cheapest class there is. Which storage class should be used?
<summary>What is "Amazon S3 Transfer Acceleration"?</summary><br><b>
AWS definition: "Amazon S3 Transfer Acceleration enables fast, easy, and secure transfers of files over long distances between your client and an S3 bucket"
Learn more [here](https://docs.aws.amazon.com/AmazonS3/latest/dev/transfer-acceleration.html)
Amazon definition: "Amazon Elastic File System (Amazon EFS) provides a simple, scalable, fully managed elastic NFS file system for use with AWS Cloud services and on-premises resources."
Learn more [here](https://aws.amazon.com/efs)
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<summary>What is AWS Snowmobile?</summary><br><b>
"AWS Snowmobile is an Exabyte-scale data transfer service used to move extremely large amounts of data to AWS."
Learn more [here](https://aws.amazon.com/snowmobile)
AWS definition: "Amazon CloudFront is a fast content delivery network (CDN) service that securely delivers data, videos, applications, and APIs to customers globally with low latency, high transfer speeds, all within a developer-friendly environment."
<summary>What is ELB (Elastic Load Balancing)?</summary><br><b>
AWS definition: "Elastic Load Balancing automatically distributes incoming application traffic across multiple targets, such as Amazon EC2 instances, containers, IP addresses, and Lambda functions."
More on ELB [here](https://aws.amazon.com/elasticloadbalancing)
<summary>What is the shared responsibility model? What AWS is responsible for and what the user is responsible for based on the shared responsibility model?</summary><br><b>
The shared responsibility model defines what the customer is responsible for and what AWS is responsible for.
More on the shared responsibility model [here](https://aws.amazon.com/compliance/shared-responsibility-model)
<summary>True or False? Based on the shared responsibility model, Amazon is responsible for physical CPUs and security groups on instances</summary><br><b>
False. It is responsible for Hardware in its sites but not for security groups which created and managed by the users.
<summary>Explain "Shared Controls" in regards to the shared responsibility model</summary><br><b>
AWS definition: "apply to both the infrastructure layer and customer layers, but in completely separate contexts or perspectives. In a shared control, AWS provides the requirements for the infrastructure and the customer must provide their own control implementation within their use of AWS services"
Learn more about it [here](https://aws.amazon.com/compliance/shared-responsibility-model)
AWS definition: "AWS Artifact is your go-to, central resource for compliance-related information that matters to you. It provides on-demand access to AWS’ security and compliance reports and select online agreements."
Read more about it [here](https://aws.amazon.com/artifact)
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<summary>What is AWS Inspector?</summary><br><b>
AWS definition: "Amazon Inspector is an automated security assessment service that helps improve the security and compliance of applications deployed on AWS. Amazon Inspector automatically assesses applications for exposure, vulnerabilities, and deviations from best practices.""
Learn more [here](https://aws.amazon.com/inspector)
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<details>
<summary>What is AWS Guarduty?</summary><br><b>
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<summary>What is AWS Shield?</summary><br><b>
AWS definition: "AWS Shield is a managed Distributed Denial of Service (DDoS) protection service that safeguards applications running on AWS."
Amazon definition: "AWS CloudHSM is a cloud-based hardware security module (HSM) that enables you to easily generate and use your own encryption keys on the AWS Cloud."
Learn more [here](https://aws.amazon.com/cloudhsm)
<summary>What is AWS Key Management Service (KMS)?</summary><br><b>
AWS definition: "KMS makes it easy for you to create and manage cryptographic keys and control their use across a wide range of AWS services and in your applications."
Amazon definition: "AWS Certificate Manager is a service that lets you easily provision, manage, and deploy public and private Secure Sockets Layer/Transport Layer Security (SSL/TLS) certificates for use with AWS services and your internal connected resources."
Learn more [here](https://aws.amazon.com/certificate-manager)
<summary>Explain "Point-in-Time Recovery" feature in DynamoDB</summary><br><b>
Amazon definition: "You can create on-demand backups of your Amazon DynamoDB tables, or you can enable continuous backups using point-in-time recovery. For more information about on-demand backups, see On-Demand Backup and Restore for DynamoDB."
Learn more [here](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/PointInTimeRecovery.html)
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<summary>Explain "Global Tables" in DynamoDB</summary><br><b>
Amazon definition: "A global table is a collection of one or more replica tables, all owned by a single AWS account."
Learn more [here](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/V2globaltables_HowItWorks.html)
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<summary>What is DynamoDB Accelerator?</summary><br><b>
Amazon definition: "Amazon DynamoDB Accelerator (DAX) is a fully managed, highly available, in-memory cache for DynamoDB that delivers up to a 10x performance improvement – from milliseconds to microseconds..."
Learn more [here](https://aws.amazon.com/dynamodb/dax)
<summary>What do you if you suspect AWS Redshift performs slowly?</summary><br><b>
* You can confirm your suspicion by going to AWS Redshift console and see running queries graph. This should tell you if there are any long-running queries.
* If confirmed, you can query for running queries and cancel the irrelevant queries
* Check for connection leaks (query for running connections and include their IP)
* Check for table locks and kill irrelevant locking sessions
<summary>What is Amazon DocumentDB?</summary><br><b>
Amazon definition: "Amazon DocumentDB (with MongoDB compatibility) is a fast, scalable, highly available, and fully managed document database service that supports MongoDB workloads. As a document database, Amazon DocumentDB makes it easy to store, query, and index JSON data."
Learn more [here](https://aws.amazon.com/documentdb)
AWS definition: "Amazon RDS Read Replicas provide enhanced performance and durability for RDS database (DB) instances. They make it easy to elastically scale out beyond the capacity constraints of a single DB instance for read-heavy database workloads."
Read more about [here](https://aws.amazon.com/rds/features/read-replicas)
[docs.aws](https://docs.aws.amazon.com/vpc/latest/peering/what-is-vpc-peering.html): "A VPC peering connection is a networking connection between two VPCs that enables you to route traffic between them using private IPv4 addresses or IPv6 addresses."
An Elastic IP address is a reserved public IP address that you can assign to any EC2 instance in a particular region, until you choose to release it.
When you associate an Elastic IP address with an EC2 instance, it replaces the default public IP address. If an external hostname was allocated to the instance from your launch settings, it will also replace this hostname; otherwise, it will create one for the instance. The Elastic IP address remains in place through events that normally cause the address to change, such as stopping or restarting the instance.
* Security Group - security layer on the instance level.
Read more about it [here](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-security-groups.html) and [here](https://docs.aws.amazon.com/vpc/latest/userguide/VPC_SecurityGroups.html)
<summary>Which service is used for sending notifications?</summary><br><b>
SNS
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<summary>What would you use for running SQL queries interactively on S3?</summary><br><b>
AWS Athena
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<summary>Which service would you use for monitoring malicious activity and unauthorized behavior in regards to AWS accounts and workloads?</summary><br><b>
Amazon GuardDuty
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<summary>Which service would you use for centrally manage billing, control access, compliance, and security across multiple AWS accounts?</summary><br><b>
AWS Organizations
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<summary>Which service would you use for web application protection?</summary><br><b>
"Amazon Route 53 is a highly available and scalable cloud Domain Name System (DNS) web service..."
Some of Route 53 features:
* Register domain
* DNS service - domain name translations
* Health checks - verify your app is available
More on Route 53 [here](https://aws.amazon.com/route53)
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#### AWS Monitoring & Logging
<details>
<summary>What is AWS CloudWatch?</summary><br><b>
AWS definition: "Amazon CloudWatch is a monitoring and observability service..."
More on CloudWatch [here](https://aws.amazon.com/cloudwatch)
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<details>
<summary>What is AWS CloudTrail?</summary><br><b>
AWS definition: "AWS CloudTrail is a service that enables governance, compliance, operational auditing, and risk auditing of your AWS account."
Read more on CloudTrail [here](https://aws.amazon.com/cloudtrail)
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<details>
<summary>What is Simply Notification Service?</summary><br><b>
AWS definition: "a highly available, durable, secure, fully managed pub/sub messaging service that enables you to decouple microservices, distributed systems, and serverless applications."
Read more about it [here](https://aws.amazon.com/sns)
<summary>What are Service Control Policies and to what service they belong?</summary><br><b>
AWS organizations service and the definition by Amazon: "SCPs offer central control over the maximum available permissions for all accounts in your organization, allowing you to ensure your accounts stay within your organization’s access control guidelines."
Learn more [here](https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_policies_scp.html)
Amazon definition: "Amazon Connect is an easy to use omnichannel cloud contact center that helps companies provide superior customer service at a lower cost."
Learn more [here](https://aws.amazon.com/connect)
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<summary>What are "APN Consulting Partners"?</summary><br><b>
Amazon definition: "APN Consulting Partners are professional services firms that help customers of all types and sizes design, architect, build, migrate, and manage their workloads and applications on AWS, accelerating their journey to the cloud."
Learn more [here](https://aws.amazon.com/partners/consulting)
<summary>What is "AWS Infrastructure Event Management"?</summary><br><b>
AWS Definition: "AWS Infrastructure Event Management is a structured program available to Enterprise Support customers (and Business Support customers for an additional fee) that helps you plan for large-scale events such as product or application launches, infrastructure migrations, and marketing events."
Amazon definition: "AWS CodeDeploy is a fully managed deployment service that automates software deployments to a variety of compute services such as Amazon EC2, AWS Fargate, AWS Lambda, and your on-premises servers."
Learn more [here](https://aws.amazon.com/codedeploy)
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<details>
<summary>Explain what is CloudFormation</summary><br><b>
AWS definition: "Lightsail is an easy-to-use cloud platform that offers you everything needed to build an application or website, plus a cost-effective, monthly plan."
<summary>What is AWS Rekognition?</summary><br><b>
AWS definition: "Amazon Rekognition makes it easy to add image and video analysis to your applications using proven, highly scalable, deep learning technology that requires no machine learning expertise to use."
Learn more [here](https://aws.amazon.com/rekognition)
<summary>What AWS Resource Groups used for?</summary><br><b>
Amazon definition: "You can use resource groups to organize your AWS resources. Resource groups make it easier to manage and automate tasks on large numbers of resources at one time. "
Learn more [here](https://docs.aws.amazon.com/ARG/latest/userguide/welcome.html)
</b></details>
<details>
<summary>What is AWS Global Accelerator?</summary><br><b>
Amazon definition: "AWS Global Accelerator is a service that improves the availability and performance of your applications with local or global users..."
Learn more [here](https://aws.amazon.com/global-accelerator)
</b></details>
<details>
<summary>What is AWS Config?</summary><br><b>
Amazon definition: "AWS Config is a service that enables you to assess, audit, and evaluate the configurations of your AWS resources."
AWS definition: "AWS X-Ray helps developers analyze and debug production, distributed applications, such as those built using a microservices architecture."
<summary>What is Amazon Cloud Directory?</summary><br><b>
Amazon definition: "Amazon Cloud Directory is a highly available multi-tenant directory-based store in AWS. These directories scale automatically to hundreds of millions of objects as needed for applications."
Learn more [here](https://docs.aws.amazon.com/clouddirectory/latest/developerguide/what_is_cloud_directory.html)
<summary>What is AWS Elastic Beanstalk?</summary><br><b>
AWS definition: "AWS Elastic Beanstalk is an easy-to-use service for deploying and scaling web applications and services...You can simply upload your code and Elastic Beanstalk automatically handles the deployment"
Learn more about it [here](https://aws.amazon.com/elasticbeanstalk)
</b></details>
<details>
<summary>What is AWS SWF?</summary><br><b>
Amazon definition: "Amazon SWF helps developers build, run, and scale background jobs that have parallel or sequential steps. You can think of Amazon SWF as a fully-managed state tracker and task coordinator in the Cloud."
Learn more on Amazon Simple Workflow Service [here](https://aws.amazon.com/swf)
AWS definition: "big data platform for processing vast amounts of data using open source tools such as Apache Spark, Apache Hive, Apache HBase, Apache Flink, Apache Hudi, and Presto."
<summary>What is AWS Quick Starts?</summary><br><b>
AWS definition: "Quick Starts are built by AWS solutions architects and partners to help you deploy popular technologies on AWS, based on AWS best practices for security and high availability."
Read more [here](https://aws.amazon.com/quickstart)
<summary>What is AWS Service Catalog?</summary><br><b>
Amazon definition: "AWS Service Catalog allows organizations to create and manage catalogs of IT services that are approved for use on AWS."
Learn more [here](https://aws.amazon.com/servicecatalog)
</b></details>
<details>
<summary>What is AWS CAF?</summary><br><b>
Amazon definition: "AWS Professional Services created the AWS Cloud Adoption Framework (AWS CAF) to help organizations design and travel an accelerated path to successful cloud adoption. "
Learn more [here](https://aws.amazon.com/professional-services/CAF)
</b></details>
<details>
<summary>What is AWS Cloud9?</summary><br><b>
AWS definition: "AWS Cloud9 is a cloud-based integrated development environment (IDE) that lets you write, run, and debug your code with just a browser"
</b></details>
<details>
<summary>What is AWS Application Discovery Service?</summary><br><b>
Amazon definition: "AWS Application Discovery Service helps enterprise customers plan migration projects by gathering information about their on-premises data centers."
Learn more [here](https://aws.amazon.com/application-discovery)
</b></details>
<details>
<summary>What is the AWS well-architected framework and what pillars it's based on?</summary><br><b>
AWS definition: "The Well-Architected Framework has been developed to help cloud architects build secure, high-performing, resilient, and efficient infrastructure for their applications. Based on five pillars — operational excellence, security, reliability, performance efficiency, and cost optimization"
Learn more [here](https://aws.amazon.com/architecture/well-architected)
<summary>What is Simple Queue Service (SQS)?</summary><br><b>
AWS definition: "Amazon Simple Queue Service (SQS) is a fully managed message queuing service that enables you to decouple and scale microservices, distributed systems, and serverless applications".
Learn more about it [here](https://aws.amazon.com/sqs)
Ethernet simply refers to the most common type of Local Area Network (LAN) used today. A LAN—in contrast to a WAN (Wide Area Network), which spans a larger geographical area—is a connected network of computers in a small area, like your office, college campus, or even home.
A MAC address is a unique identification number or code used to identify individual devices on the network.
Packets that are sent on the ethernet are always coming from a MAC address and sent to a MAC address. If a network adapter is receiving a packet, it is comparing the packet’s destination MAC address to the adapter’s own MAC address.
When a device sends a packet to the broadcast MAC address (FF:FF:FF:FF:FF:FF), it is delivered to all stations on the local network. It needs to be used in order for all devices to receive your packet at the datalink layer.
An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.An IP address serves two main functions: host or network interface identification and location addressing.
A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s. Within a given network, two host addresses are reserved for special purpose, and cannot be assigned to hosts. The "0" address is assigned a network address and "255" is assigned to a broadcast address, and they cannot be assigned to hosts.
A router is a physical or virtual appliance that passes information between two or more packet-switched computer networks. A router inspects a given data packet's destination Internet Protocol address (IP address), calculates the best way for it to reach its destination and then forwards it accordingly.
Network Address Translation (NAT) is a process in which one or more local IP address is translated into one or more Global IP address and vice versa in order to provide Internet access to the local hosts.
A proxy server acts as a gateway between you and the internet. It’s an intermediary server separating end users from the websites they browse.
If you’re using a proxy server, internet traffic flows through the proxy server on its way to the address you requested. The request then comes back through that same proxy server (there are exceptions to this rule), and then the proxy server forwards the data received from the website to you.
roxy servers provide varying levels of functionality, security, and privacy depending on your use case, needs, or company policy.
TCP 3-way handshake or three-way handshake is a process which is used in a TCP/IP network to make a connection between server and client.
A three-way handshake is primarily used to create a TCP socket connection. It works when:
- A client node sends a SYN data packet over an IP network to a server on the same or an external network. The objective of this packet is to ask/infer if the server is open for new connections.
- The target server must have open ports that can accept and initiate new connections. When the server receives the SYN packet from the client node, it responds and returns a confirmation receipt – the ACK packet or SYN/ACK packet.
- The client node receives the SYN/ACK from the server and responds with an ACK packet.
<summary>What is round-trip delay or round-trip time?</summary><br><b>
From [wikipedia](https://en.wikipedia.org/wiki/Round-trip_delay): "the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgement of that signal to be received"
TCP establishes a connection between the client and the server to guarantee the order of the packages, on the other hand, UDP does not establish a connection between client and server and doesn't handle package order. This makes UDP more lightweight than TCP and a perfect candidate for services like streaming.
[Penguintutor.com](http://www.penguintutor.com/linux/basic-network-reference) provides a good explanation.
A default gateway serves as an access point or IP router that a networked computer uses to send information to a computer in another network or the internet.
ARP stands for Address Resolution Protocol. When you try to ping an IP address on your local network, say 192.168.1.1, your system has to turn the IP address 192.168.1.1 into a MAC address. This involves using ARP to resolve the address, hence its name.
Systems keep an ARP look-up table where they store information about what IP addresses are associated with what MAC addresses. When trying to send a packet to an IP address, the system will first consult this table to see if it already knows the MAC address. If there is a value cached, ARP is not used.
<summary>What is NAT? How does it work?</summary><br><b>
NAT stands for network address translation. It’s a way to map multiple local private addresses to a public one before transferring the information. Organizations that want multiple devices to employ a single IP address use NAT, as do most home routers.
For example, your computer's private IP could be 192.168.1.100, but your router maps the traffic to it's public IP (e.g. 1.1.1.1). Any device on the internet would see the traffic coming from your public IP (1.1.1.1) instead of your private IP (192.168.1.100).
<summary>What the terms "Data Plane" and "Control Plane" refer?</summary><br><b>
The exact meaning is usually depends on the context but overall data plane refers to all the functions that forward packets and/or frames from one interface to another while control plane refers to all the functions that make use of routing protocols.
There is also "Management Plane" which refers to monitoring and management functions.
<summary>When performing a search query, what is more important, latency or throughput? And how to assure that what managing global infrastructure?</summary><br><b>
Latency. To have a good latency, a search query should be forwarded to the closest datacenter.
</b></details>
<details>
<summary>When uploading a video, what is more important, latency or throughput? And how to assure that?</summary><br><b>
Throughput. To have a good throughput, the upload stream should be routed to an underutilized link.
</b></details>
<details>
<summary>What other considerations (except latency and throughput) are there when forwarding requests?</summary><br><b>
* Keep caches updated (which means the request could be forwarded not to the closest datacenter)
HTTP Strict Transport Security is a web server directive that informs user agents and web browsers how to handle its connection through a response header sent at the very beginning and back to the browser. This forces connections over HTTPS encryption, disregarding any script's call to load any resource in that domain over HTTP.
Read more [here](https://www.globalsign.com/en/blog/what-is-hsts-and-how-do-i-use-it#:~:text=HTTP%20Strict%20Transport%20Security%20(HSTS,and%20back%20to%20the%20browser.)
</b></details>
<details>
<summary>What is the difference if any between SSL and TLS?</summary><br><b>
<summary>Some of the commands in the previous question can be run with the -r/-R flag. What does it do? Give an example to when you would use it</summary><br><b>
The -r (or -R in some commands) flag allows user to run a certain command recursively. For example, listing all the files under the following tree is possible when done recursively (`ls -R`):
These are files directly not displayed after performing a standard ls direct listing. An example of these files are .bashrc which are used to execute some scripts. Some also store configuration about services on your host like .KUBECONFIG. The command used to list them is, `ls -a`
3. You would look for your distro default $PATH variable, copy paste using method #1
Note: There are many ways of getting errors like this: if bash_profile or any configuration file of your interpreter was wrongly modified; causing erratics behaviours,
* setuid is a linux file permission that permits a user to run a file or program with the permissions of the owner of that file. This is possible by elevation of current user privileges.
<summary>What this line in scripts mean?: <code>#!/bin/bash</code></summary><br><b>
`#!/bin/bash` is She-bang
/bin/bash is the most common shell used as default shell for user login of the linux system. The shell’s name is an acronym for Bourne-again shell. Bash can execute the vast majority of scripts and thus is widely used because it has more features, is well developed and better syntax.
</b></details>
<details>
<summary>True or False?: when a certain command/line fails, the script, by default, will exit and will no keep running</summary><br><b>
Depends on the language and settings used.
When a script written in Bash fails to run a certain command it will keep running and will execute all other commands mentioned after the command which failed.
Most of the time we would actually want the opposite to happen. In order to make Bash exist when a specific command fails, use 'set -e' in your script.
</b></details>
<details>
<summary>Explain what would be the result of each command:
*<code>echo $0</code>
*<code>echo $?</code>
*<code>echo $$</code>
*<code>echo $@</code>
*<code>echo $#</code></summary><br><b>
</b></details>
<details>
<summary>How do you debug shell scripts?</summary><br><b>
Answer depends on the language you are using for writing your scripts. If Bash is used for example then:
* Adding -x to the script I'm running in Bash
* Old good way of adding echo statements
If Python, then using pdb is very useful.
</b></details>
<details>
<summary>How do you get input from the user in shell scripts?</summary><br><b>
Using the keyword <code>read</code> so for example <code>read x</code> will wait for user input and will store it in the variable x.
</b></details>
<details>
<summary>Explain <code>continue</code> and <code>break</code>. When do you use them if at all?</summary><br><b>
</b></details>
<details>
<summary>Running the following bash script, we don't get 2 as a result, why?
```
x = 2
echo $x
```
</summary><br><b>
Should be `x=2`
</b></details>
<details>
<summary>How to store the output of a command in a variable?</summary><br><b>
</b></details>
<details>
<summary>How do you check variable length?</summary><br><b>
</b></details>
<details>
<summary>Explain the following code:
<code>:(){ :|:& };:</code>
</summary><br><b>
</b></details>
<details>
<summary>Can you give an example to some Bash best practices?</summary><br><b>
</b></details>
<details>
<summary>What is the ternary operator? How do you use it in bash?</summary><br><b>
A short way of using if/else. An example:
[[ $a = 1 ]] && b="yes, equal" || b="nope"
</b></details>
<details>
<summary>What does the following code do and when would you use it?
<code>diff <(ls /tmp) <(ls /var/tmp)</code>
</summary><br>
It is called 'process substitution'. It provides a way to pass the output of a command to another command when using a pipe <code>|</code> is not possible. It can be used when a command does not support <code>STDIN</code> or you need the output of multiple commands.
<summary>Explain user space vs. kernel space</summary><br><b>
The operating system executes the kernel in protected memory to prevent anyone from changing (and risking it crashing). This is what is known as "Kernel space".
"User space" is where users executes their commands or applications. It's important to create this separation since we can't rely on user applications to not tamper with the kernel, causing it to crash.
Applications can access system resources and indirectly the kernel space by making what is called "system calls".
</b></details>
#### Linux Virtualization
<details>
<summary>What virtualization solutions are available for Linux?</summary><br><b>
<summary>What is SSH? How to check if a Linux server is running SSH?</summary><br><b>
[Wikipedia Definition](https://en.wikipedia.org/wiki/SSH_(Secure_Shell)): "SSH or Secure Shell is a cryptographic network protocol for operating network services securely over an unsecured network."
[Hostinger.com Definition](https://www.hostinger.com/tutorials/ssh-tutorial-how-does-ssh-work): "SSH, or Secure Shell, is a remote administration protocol that allows users to control and modify their remote servers over the Internet."
An SSH server will have SSH daemon running. Depends on the distribution, you should be able to check whether the service is running (e.g. systemctl status sshd).
</b></details>
<details>
<summary>Why SSH is considered better than telnet?</summary><br><b>
Telnet also allows you to connect to a remote host but as opposed to SSH where the communication is encrypted, in telnet, the data is sent in clear text, so it doesn't considered to be secured because anyone on the network can see what exactly is sent, including passwords.
</b></details>
<details>
<summary>What is stored in <code>~/.ssh/known_hosts</code>?</summary><br><b>
</b></details>
<details>
<summary>You try to ssh to a server and you get "Host key verification failed". What does it mean?</summary><br><b>
It means that the key of the remote host was changed and doesn't match the one that stored on the machine (in ~/.ssh/known_hosts).
<summary>You are trying to create a new file but you get "File system is full". You check with df for free space and you see you used only 20% of the space. What could be the problem?</summary><br><b>
execution or run forever, you may want to run them in the background instead of waiting for them to finish before gaining control again in current session.
A process which has finished to run but has not exited.
One reason it happens is when a parent process is programmed incorrectly. Every parent process should execute wait() to get the exit code from the child process which finished to run. But when the parent isn't checking for the child exit code, the child process can still exists although it finished to run.
<summary>How to get rid of zombie processes?</summary><br><b>
You can't kill a zombie process the regular way with `kill -9` for example as it's already dead.
One way to kill zombie process is by sending SIGCHLD to the parent process telling it to terminate its child processes. This might not work if the parent process wasn't programmed properly. The invocation is `kill -s SIGCHLD [parent_pid]`
You can also try closing/terminating the parent process. This will make the zombie process a child of init (1) which does periodic cleanups and will at some point clean up the zombie process.
It is the first process executed by the kernel during the booting of a system. It is a daemon process which runs till the system is shutdown. That is why, it is the parent of all the processes
The loopback interface is a special, virtual network interface that your computer uses to communicate with itself. It is used mainly for diagnostics and troubleshooting, and to connect to servers running on the local machine.
Telnet is a type of client-server protocol that can be used to open a command line on a remote computer, typically a server.
By default, all the data sent and received via telnet is transmitted in clear/plain text, therefore it should not be used as it does not encrypt any data between the client and the server.
In addition, you can specify in a spec how a certain package will be installed - where to copy the files, which commands to run prior to the installation, post the installation, etc.
<summary>What a double dash (--) mean?</summary><br><b>
It's used in commands to mark the end of commands options. One common example is when used with git to discard local changes: `git checkout -- some_file`
fork() is used for creating a new process. It does so by cloning the calling process but the child process has its own PID and any memory locks, I/O operations and semaphores are not inherited.
<summary>How the kernel notifies the parent process about child process termination?</summary><br><b>
The kernel notifies the parent by sending the SIGCHLD to the parent.
</b></details>
<details>
<summary>How the waitpid() is different from wait()?</summary><br><b>
The waitpid() is a non-blocking version of the wait() function.<br>
It also supports using library routine (e.g. system()) to wait a child process without messing up with other children processes for which the process has not waited.
<summary>Explain the exec() system call</summary><br><b>
It transforms the current running program into another program.<br>
Given the name of an executable and some arguments, it loads the code and static data from the specified executable and overwrites its current code segment and current static code data. After initializing its memory space (like stack and heap) the OS runs the program passing any arguments as the argv of that process.
"Pipes provide a unidirectional interprocess communication channel. A pipe has a read end and a write end. Data written to the write end of a pipe can be read from the read end of the pipe.
A pipe is created using pipe(2), which returns two file descriptors, one referring to the read end of the pipe, the other referring to the write end."
<summary>Why running a new program is done using the fork() and exec() system calls? why a different API wasn't developed where there is one call to run a new program?</summary><br><b>
This way provides a lot of flexibility. It allows the shell for example, to run code after the call to fork() but before the call to exec(). Such code can be used to alter the environment of the program it about to run.
</b></details>
<details>
<summary>Describe shortly what happens when you execute a command in the shell</summary><br><b>
The shell figures out, using the PATH variable, where the executable of the command resides in the filesystem. It then calls fork() to create a new child process for running the command. Once the fork was executed successfully, it calls a variant of exec() to execute the command and finally, waits the command to finish using wait(). When the child completes, the shell returns from wait() and prints out the prompt again.
From [wikipedia](https://en.wikipedia.org/wiki/Context_switch): a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point
<summary>You executed a script and while still running, it got accidentally removed. Is it possible to restore the script while it's still running?</summary><br><b>
<summary>What is the difference between MemFree and MemAvailable in /proc/meminfo?</summary><br><b>
MemFree - The amount of unused physical RAM in your system
MemAvailable - The amount of available memory for new workloads (without pushing system to use swap) based on MemFree, Active(file), Inactive(file), and SReclaimable.
"responsible for making it easy to run programs (even allowing you to seemingly run many at the same time), allowing programs to share memory, enabling programs to interact with devices, and other fun stuff like that".
* Memory is allocated for program's stack (aka run-time stack). The stack also initialized by the OS with data like argv, argc and parameters to main()
<summary>True or False? The loading of the program into the memory is done eagerly (all at once)</summary><br><b>
False. It was true in the past but today's operating systems perform lazy loading which means only the relevant pieces required for the process to run are loaded first.
Even when using a system with one physical CPU, it's possible to allow multiple users to work on it and run programs. This is possible with time sharing where computing resources are shared in a way it seems to the user the system has multiple CPUs but in fact it's simply one CPU shared by applying multiprogramming and multi-tasking.
<summary>What is "space sharing"?</summary><br><b>
Somewhat the opposite of time sharing. While in time sharing a resource is used for a while by one entity and then the same resource can be used by another resource, in space sharing the space is shared by multiple entities but in a way where it's not being transferred between them.<br>
It's used by one entity until this entity decides to get rid of it. Take for example storage. In storage, a file is yours until you decide to delete it.
<summary>What component determines which process runs at a given moment in time?</summary><br><b>
CPU scheduler
</b></details>
#### Operating System - Memory
<details>
<summary>What is "virtual memory" and what purpose it serves?</summary><br><b>
</b></details>
<details>
<summary>What is demand paging?</summary><br><b>
</b></details>
<details>
<summary>What is copy-on-write or shadowing?</summary><br><b>
</b></details>
<details>
<summary>What is a kernel, and what does it do?</summary><br><b>
The kernel is part of the operating system and is responsible for tasks like:
* Allocating memory
* Schedule processes
* Control CPU
</b></details>
<details>
<summary>True or False? Some pieces of the code in the kernel are loaded into protected areas of the memory so applications can't overwritten them</summary><br><b>
True
</b></details>
<details>
<summary>What is POSIX?</summary><br><b>
</b></details>
<details>
<summary>Explain what is Semaphore and what its role in operating systems</summary><br><b>
<summary>What is cache? What is buffer?</summary><br><b>
Buffer: Reserved place in RAM which is used to hold data for temporary purposes
Cache: Cache is usually used when processes reading and writing to the disk to make the process faster by making similar data used by different programs easily accessible.
Virtualization uses software to create an abstraction layer over computer hardware that allows the hardware elements of a single computer—processors, memory, storage and more - to be divided into multiple virtual computers, commonly called virtual machines (VMs).
Red Hat: "A hypervisor is software that creates and runs virtual machines (VMs). A hypervisor, sometimes called a virtual machine monitor (VMM), isolates the hypervisor operating system and resources from the virtual machines and enables the creation and management of those VMs."
Read more [here](https://www.redhat.com/en/topics/virtualization/what-is-a-hypervisor)
</b></details>
<details>
<summary>What types of hypervisors are there?</summary><br><b>
Hosted hypervisors and bare-metal hypervisors.
</b></details>
<details>
<summary>What are the advantages and disadvantges of bare-metal hypervisor over a hosted hypervisor?</summary><br><b>
Due to having its own drivers and a direct access to hardware components, a baremetal hypervisor will often have better performances along with stability and scalability.
On the other hand, there will probably be some limitation regarding loading (any) drivers so a hosted hypervisor will usually benefit from having a better hardware compatibility.
</b></details>
<details>
<summary>What types of virtualization are there?</summary><br><b>
Operating system virtualization
Network functions virtualization
Desktop virtualization
</b></details>
<details>
<summary>Is containerization is a type of Virtualization?</summary><br><b>
Yes, it's a operating-system-level virtualization, where the kernel is shared and allows to use multiple isolated user-spaces instances.
Module – the actual unit of code executed by Ansible on your own host or a remote host. Modules are indexed by category (database, file, network, …) and also referred to as task plugins.
Play – One or more tasks executed on a given host(s)
Playbook – One or more plays. Each play can be executed on the same or different hosts
Role – Ansible roles allows you to group resources based on certain functionality/service such that they can be easily reused. In a role, you have directories for variables, defaults, files, templates, handlers, tasks, and metadata. You can then use the role by simply specifying it in your playbook.
True. In immutable infrastructure approach, you'll replace infrastructure instead of modifying it.<br>
Ansible rather follows the mutable infrastructure paradigm where it allows you to change the configuration of different components, but this approach is not perfect and has its own disadvantges like "configuration drift" where different components may reach different state for different reasons.
additional check is implemented or explicit names are provided) while other tools might check if 5 instances exist. If only 4 exist (by checking the state file for example), one additional instance will be created to reach the end goal of 5 instances.
When given a written code, always inspect it thoroughly. If your answer is “this will fail” then you are right. We are using a fact (ansible_hostname), which is a gathered piece of information from the host we are running on. But in this case, we disabled facts gathering (gather_facts: no) so the variable would be undefined which will result in failure.
<summary>The value of a certain variable you use is the string "True". You would like the value to be a boolean. How would you cast it?</summary><br><b>
<summary>The variable 'whoami' defined in the following places:
* role defaults -> whoami: mario
* extra vars (variables you pass to Ansible CLI with -e) -> whoami: toad
* host facts -> whoami: luigi
* inventory variables (doesn’t matter which type) -> whoami: browser
According to variable precedence, which one will be used?</summary><br><b>
The right answer is ‘toad’.
Variable precedence is about how variables override each other when they set in different locations. If you didn’t experience it so far I’m sure at some point you will, which makes it a useful topic to be aware of.
In the context of our question, the order will be extra vars (always override any other variable) -> host facts -> inventory variables -> role defaults (the weakest).
A full list can be found at [PlayBook Variables](https://docs.ansible.com/ansible/latest/user_guide/playbooks_variables.html#ansible-variable-precedence) . Also, note there is a significant difference between Ansible 1.x and 2.x.
<summary>Explain the Diffrence between Forks and Serial & Throttle.</summary><br><b>
`Serial` is like running the playbook for each host in turn, waiting for completion of the complete playbook before moving on to the next host. `forks`=1 means run the first task in a play on one host before running the same task on the next host, so the first task will be run for each host before the next task is touched. Default fork is 5 in ansible.
```
[defaults]
forks = 30
```
```
- hosts: webservers
serial: 1
tasks:
- name: ...
```
Ansible also supports `throttle` This keyword limits the number of workers up to the maximum set via the forks setting or serial. This can be useful in restricting tasks that may be CPU-intensive or interact with a rate-limiting API
<summary>True or False? By default, Ansible will execute all the tasks in play on a single host before proceeding to the next host</summary><br><b>
False. Ansible will execute a single task on all hosts before moving to the next task in a play. As for today, it uses 5 forks by default.<br>
This behaviour is described as "strategy" in Ansible and it's configurable.
</b></details>
<details>
<summary>What is a "strategy" in Ansible? What is the default strategy?</summary><br><b>
A strategy in Ansible describes how Ansible will execute the different tasks on the hosts. By default Ansible is using the "Linear strategy" which defines that each task will run on all hosts before proceeding to the next task.
</b></details>
<details>
<summary>What strategies are you familiar with in Ansible?</summary><br><b>
- Linear: the default strategy in Ansible. Run each task on all hosts before proceeding.
- Free: For each host, run all the tasks until the end of the play as soon as possible
- Debug: Run tasks in an interactive way
</b></details>
<details>
<summary>What the <code>serial</code> keyword is used for?</summary><br><b>
It's used to specify the number (or percentage) of hosts to run the full play on, before moving to next number of hosts in the group.
For example:
```
- name: Some play
hosts: databases
serial: 4
```
If your group has 8 hosts. It will run the whole play on 4 hosts and then the same play on another 4 hosts.
[Terraform.io](https://www.terraform.io/intro/index.html#what-is-terraform-): "Terraform is an infrastructure as code (IaC) tool that allows you to build, change, and version infrastructure safely and efficiently."<br>
* Ansible and Puppet are more procedural (you mention what to execute in each step) and Terraform is declarative since you describe the overall desired state and not per resource or task. You can give the example of going from 1 to 2 servers in each tool. In Terraform you specify 2, in Ansible and puppet you have to only provision 1 additional server so you need to explicitly make sure you provision only another one server.
HCL stands for Hashicorp Configuration Language. It is the language Hashicorp made to use as the configuration language for a number of its tools, including terraform.
HashiCorp: "Terraform uses resource blocks to manage infrastructure, such as virtual networks, compute instances, or higher-level components such as DNS records. Resource blocks represent one or more infrastructure objects in your Terraform configuration."
</b></details>
<details>
<summary>Explain each part of the following line: `resource "aws_instance" "web_server" {...}`</summary><br><b>
- resource: keyword for defining a resource
- "aws_instance": the type of the resource
- "web_server": the name of the resource
</b></details>
<details>
<summary>What is the ID of the following resource: `resource "aws_instance" "web_server" {...}`</summary><br><b>
`aws_instance.web_server`
</b></details>
<details>
<summary>True or False? Resource ID must be unique within a workspace</summary><br><b>
- Attributes: values exposed by the resource in a form of `resource_type.resource_name.attribute_name`. They are set by the provider or API usually.
- Meta-arguments: Functions of Terraform to change resource's behaviour
</b></details>
#### Terraform - Providers
<details>
<summary>Explain what is a "provider"</summary><br><b>
[terraform.io](https://www.terraform.io/docs/language/providers/index.html): "Terraform relies on plugins called "providers" to interact with cloud providers, SaaS providers, and other APIs...Each provider adds a set of resource types and/or data sources that Terraform can manage. Every resource type is implemented by a provider; without providers, Terraform can't manage any kind of infrastructure."
</b></details>
<details>
<summary>What is the name of the provider in this case: `resource "libvirt_domain" "instance" {...}`</summary><br><b>
libvirt
</b></details>
#### Terraform - Variables
<details>
<summary>What are Input Variables in Terraform? Why one should use them?</summary><br><b>
Input variables serve as parameters to the module in Terraform. They allow you for example to define once the value of a variable and use that variable in different places in the module so next time you would want to change the value, you will change it in one place instead of changing the value in different places in the module.
</b></details>
<details>
<summary>How to define variables?</summary><br><b>
```
variable "app_id" {
type = string
description = "The id of application"
default = "some_value"
}
```
Usually they are defined in their own file (vars.tf for example).
</b></details>
<details>
<summary>How variables are used in modules?</summary><br><b>
They are referenced with `var.VARIABLE_NAME`
vars.tf:
```
variable "memory" {
type = string
default "8192"
}
variable "cpu" {
type = string
default = "4"
}
```
main.tf:
```
resource "libvirt_domain" "vm1" {
name = "vm1"
memory = var.memory
cpu = var.cpu
}
```
</b></details>
<details>
<summary>How would you enforce users that use your variables to provide values with certain constraints? For example, a number greater than 1</summary><br><b>
Using `validation` block
```
variable "some_var" {
type = number
validation {
condition = var.some_var > 1
error_message = "you have to specify a number greater than 1"
}
}
```
</b></details>
<details>
<summary>What is the effect of setting variable as "sensitive"?</summary><br><b>
It doesn't show its value when you run `terraform apply` or `terraform plan` but eventually it's still recorded in the state file.
</b></details>
<details>
<summary>True or Fales? If an expression's result depends on a sensitive variable, it will be treated as sensitive as well</summary><br><b>
True
</b></details>
<details>
<summary>The same variable is defined in the following places:
- The file `terraform.tfvars`
- Environment variable
- Using `-var` or `-var-file`
According to varaible precedence, which source will be used first?</summary><br><b>
The order is:
- Environment variable
- The file `terraform.tfvars`
- Using `-var` or `-var-file`
</b></details>
<details>
<summary>What other way is there to define lots of variables in more "simplified" way?</summary><br><b>
Using `.tfvars` file which contains variable consists of simple variable names assignments this way:
- tfstate contains credentials in plain text. You don't want to put it in publicly shared location
- tfstate shouldn't be modified concurrently so putting it in a shared location available for everyone with "write" permissions might lead to issues. (Terraform remote state doesn't has this problem).
- tfstate is in important file. As such, it might be better to put it in a location that has regular backups.
<summary>You've deployed a virtual machine with Terraform and you would like to pass data to it (or execute some commands). Which concept of Terraform would you use?</summary><br><b>
<summary>What are "Provisioners"? What they are used for?</summary><br><b>
Provisioners used to execute actions on local or remote machine. It's extremely useful in case you provisioned an instance and you want to make a couple of changes in the machine you've created without manually ssh into it after Terraform finished to run and manually run them.
<code>terraform taint resource.id</code> manually marks the resource as tainted in the state file. So when you run <code>terraform apply</code> the next time, the resource will be destroyed and recreated.
Output variables are named values that are sourced from the attributes of a module. They are stored in terraform state, and can be used by other modules through <code>remote_state</code>
A Terraform module is a set of Terraform configuration files in a single directory. Modules are small, reusable Terraform configurations that let you manage a group of related resources as if they were a single resource. Even a simple configuration consisting of a single directory with one or more .tf files is a module. When you run Terraform commands directly from such a directory, it is considered the root module. So in this sense, every Terraform configuration is part of a module.
State locking is a mechanism that blocks an operations against a specific state file from multiple callers so as to avoid conflicting operations from different team members. Once the first caller's operation's lock is released the other team member may go ahead to
carryout his own operation. Nevertheless Terraform will first check the state file to see if the desired resource already exist and
<summary>How do you test a terraform module?</summary><br><b>
Many examples are acceptable, but the most common answer would likely to be using the tool <code>terratest</code>, and to test that a module can be initialized, can create resources, and can destroy those resources cleanly.
</b></details>
<details>
<summary>Aside from <code>.tfvars</code> files or CLI arguments, how can you inject dependencies from other modules?</summary><br><b>
The built-in terraform way would be to use <code>remote-state</code> to lookup the outputs from other modules.
It is also common in the community to use a tool called <code>terragrunt</code> to explicitly inject variables between modules.
Containers are a form of operating system virtualization. A single container might be used to run anything from a small microservice or software process to a larger application. Inside a container are all the necessary executables, binary code, libraries, and configuration files, making them easy to ship and run with same expected results on different machines.
* It usually takes a few seconds to set up a container as opposed to VMs which can take minutes or at least more time than containers as there is an entire OS to boot and initialize as opposed to container where you mainly lunch the app itself
* Containers are isolated from each other, but not as concretely as virtual machines. It is possible for a malicious user to break into the host OS from a container and vice versa.
<summary>What are `dockerd, docker-containerd, docker-runc, docker-containerd-ctr, docker-containerd-shim` ?</summary><br><b>
dockerd - The Docker daemon itself. The highest level component in your list and also the only 'Docker' product listed. Provides all the nice UX features of Docker.
(docker-)containerd - Also a daemon, listening on a Unix socket, exposes gRPC endpoints. Handles all the low-level container management tasks, storage, image distribution, network attachment, etc...
(docker-)containerd-ctr - A lightweight CLI to directly communicate with containerd. Think of it as how 'docker' is to 'dockerd'.
(docker-)runc - A lightweight binary for actually running containers. Deals with the low-level interfacing with Linux capabilities like cgroups, namespaces, etc...
(docker-)containerd-shim - After runC actually runs the container, it exits (allowing us to not have any long-running processes responsible for our containers). The shim is the component which sits between containerd and runc to facilitate this.
<summary>Describe difference between cgroups and namespaces </summary><br><b>
cgroup: Control Groups provide a mechanism for aggregating/partitioning sets of tasks, and all their future children, into hierarchical groups with specialized behaviour.
namespace: wraps a global system resource in an abstraction that makes it appear to the processes within the namespace that they have their own isolated instance of the global resource.
In short:
Cgroups = limits how much you can use;
namespaces = limits what you can see (and therefore use)
Cgroups involve resource metering and limiting:
memory
CPU
block I/O
network
Namespaces provide processes with their own view of the system
Multiple namespaces: pid,net, mnt, uts, ipc, user
</b></details>
<details>
<summary>Describe in detail what happens when you run `docker pull image:tag`?</summary><br><b>
Docker CLI passes your request to Docker daemon. Dockerd Logs shows the process
docker.io/library/busybox:latest resolved to a manifestList object with 9 entries; looking for a unknown/amd64 match
found match for linux/amd64 with media type application/vnd.docker.distribution.manifest.v2+json, digest sha256:400ee2ed939df769d4681023810d2e4fb9479b8401d97003c710d0e20f7c49c6
pulling blob \"sha256:61c5ed1cbdf8e801f3b73d906c61261ad916b2532d6756e7c4fbcacb975299fb Downloaded 61c5ed1cbdf8 to tempfile /var/lib/docker/tmp/GetImageBlob909736690
Applying tar in /var/lib/docker/overlay2/507df36fe373108f19df4b22a07d10de7800f33c9613acb139827ba2645444f7/diff" storage-driver=overlay2
Applied tar sha256:514c3a3e64d4ebf15f482c9e8909d130bcd53bcc452f0225b0a04744de7b8c43 to 507df36fe373108f19df4b22a07d10de7800f33c9613acb139827ba2645444f7, size: 1223534
1. To remove one or more Docker images use the docker container rm command followed by the ID of the containers you want to remove.
2. The docker system prune command will remove all stopped containers, all dangling images, and all unused networks
3. docker rm $(docker ps -a -q) - This command will delete all stopped containers. The command docker ps -a -q will return all existing container IDs and pass them to the rm command which will delete them. Any running containers will not be deleted.
Docker can build images automatically by reading the instructions from a Dockerfile. A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image.
COPY takes in a src and destination. It only lets you copy in a local file or directory from your host (the machine building the Docker image) into the Docker image itself.
ADD lets you do that too, but it also supports 2 other sources. First, you can use a URL instead of a local file / directory. Secondly, you can extract a tar file from the source directly into the destination.
Although ADD and COPY are functionally similar, generally speaking, COPY is preferred. That’s because it’s more transparent than ADD. COPY only supports the basic copying of local files into the container, while ADD has some features (like local-only tar extraction and remote URL support) that are not immediately obvious.
RUN lets you execute commands inside of your Docker image. These commands get executed once at build time and get written into your Docker image as a new layer.
CMD is the command the container executes by default when you launch the built image. A Dockerfile can only have one CMD.
You could say that CMD is a Docker run-time operation, meaning it’s not something that gets executed at build time. It happens when you run an image. A running image is called a container.
Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, with a single command, you create and start all the services from your configuration.
A Docker image is built up from a series of layers. Each layer represents an instruction in the image’s Dockerfile. Each layer except the very last one is read-only.
Each layer is only a set of differences from the layer before it. The layers are stacked on top of each other. When you create a new container, you add a new writable layer on top of the underlying layers. This layer is often called the “container layer”. All changes made to the running container, such as writing new files, modifying existing files, and deleting files, are written to this thin writable container layer.
The major difference between a container and an image is the top writable layer. All writes to the container that add new or modify existing data are stored in this writable layer. When the container is deleted, the writable layer is also deleted. The underlying image remains unchanged.
Because each container has its own writable container layer, and all changes are stored in this container layer, multiple containers can share access to the same underlying image and yet have their own data state.
* You would like to run a certain application in a container on multiple different locations. Sure, if it's 2-3 servers/locations, you can do it by yourself but it can be challenging to scale it up to additional multiple location.<br>
* Performing updates and changes across hundreds of containers<br>
Red Hat Definition: "A Kubernetes cluster is a set of node machines for running containerized applications. If you’re running Kubernetes, you’re running a cluster.
At a minimum, a cluster contains a worker node and a master node."
Read more [here](https://www.redhat.com/en/topics/containers/what-is-a-kubernetes-cluster)
</b></details>
<details>
<summary>Do you have experience with deploying a Kubernetes cluster? If so, can you describe the process in high-level?</summary><br><b>
1. Create multiple instances you will use as Kubernetes nodes/workers. Create also an instance to act as the Master. The instances can be part of the cloud or virtual machines on physical hosts.
Kubectl is the Kubernetes command line tool that allows you to run commands against Kubernetes clusters. For example, you can use kubectl to deploy applications, inspect and manage cluster resources, and view logs.
If you are a Kubernetes beginner you should know that this is not a common way to run Pods. The common way is to run a Deployment which in turn runs Pod(s).
False. By default, pods are non-isolated = pods accept traffic from any source.
</b></details>
<details>
<summary>True or False? The "Pending" phase means the Pod was not yet accepted by the Kubernetes cluster so the scheduler can't run it unless it's accepted</summary><br><b>
False. "Pending" is after the Pod was accepted by the cluster, but the container can't run for different reasons like images not yet downloaded.
* For each static Pod there is a mirror Pod on kubernetes API server but it can't be managed from there
Read more about it [here](https://kubernetes.io/docs/tasks/configure-pod-container/static-pod)
</b></details>
<details>
<summary>What happens when you run a Pod?</summary><br><b>
1. Kubectl sends a request to the API server to create the Pod
2. The Scheduler detects that there is an unassigned Pod (by monitoring the API server)
3. The Scheduler chooses a node to assign the Pod to
4. The Scheduler updates the API server about which node it chose
5. Kubelet (which also monitors the API server) notices there is a Pod assigned to the same node on which it runs and that Pod isn't running
6. Kubelet sends request to the container engine (e.g. Docker) to create and run the containers
7. An update is sent by Kubelet to the API server (notifying it that the Pod is running)
</b></details>
<details>
<summary>How to confirm a container is running after running the command <code>kubectl run web --image nginxinc/nginx-unprivileged</code></summary><br><b>
* When you run `kubectl describe pods <POD_NAME>` it will tell whether the container is running:
`Status: Running`
* Run a command inside the container: `kubectl exec web -- ls`
</b></details>
<details>
<summary>After running <code>kubectl run database --image mongo</code> you see the status is "CrashLoopBackOff". What could possibly went wrong and what do you do to confirm?</summary><br><b>
"CrashLoopBackOff" means the Pod is starting, crashing, starting...and so it repeats itself.<br>
One of the ways to check why it happened it to run `kubectl describe po <POD_NAME>` and having a look at the exit code
```
Last State: Terminated
Reason: Error
Exit Code: 100
```
Another way to look into it, is to run `kubectl logs <POD_NAME>`. This will provide us with the logs from the containers running in that Pod.
</b></details>
<details>
<summary>What does the "ErrImagePull" status of a Pod means?</summary><br><b>
It wasn't able to pull the image specified for running the container(s). This can happen if the client didn't authenticated for example.<br>
More details can be obtained with `kubectl describe po <POD_NAME>`.
A Kubernetes Deployment is used to tell Kubernetes how to create or modify instances of the pods that hold a containerized application.
Deployments can scale the number of replica pods, enable rollout of updated code in a controlled manner, or roll back to an earlier deployment version if necessary.
A Deployment is a declarative statement for the desired state for Pods and Replica Sets.
"An abstract way to expose an application running on a set of Pods as a network service." - read more [here](https://kubernetes.io/docs/concepts/services-networking/service)
In simpler words, it allows you to expose the service by attaching permanent IP address for example to a certain pod.
</b></details>
<details>
<summary>True or False? The lifecycle of Pods and Services isn't connected so when a pod dies, the service still stays </summary><br><b>
From Kubernetes docs: "Ingress exposes HTTP and HTTPS routes from outside the cluster to services within the cluster. Traffic routing is controlled by rules defined on the Ingress resource."
Read more [here](https://kubernetes.io/docs/concepts/services-networking/ingress/)
<summary>Complete the following configuration file to make it Ingress
```
metadata:
name: someapp-ingress
spec:
```
</summary><br><b>
There are several ways to answer this question.
```
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: someapp-ingress
spec:
rules:
- host: my.host
http:
paths:
- backend:
serviceName: someapp-internal-service
servicePort: 8080
```
</b></details>
<details>
<summary>Explain the meaning of "http", "host" and "backend" directives
```
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: someapp-ingress
spec:
rules:
- host: my.host
http:
paths:
- backend:
serviceName: someapp-internal-service
servicePort: 8080
```
</summary><br><b>
host is the entry point of the cluster so basically a valid domain address that maps to cluster's node IP address<br>
the http line used for specifying that incoming requests will be forwarded to the internal service using http.<br>
backend is referencing the internal service (serviceName is the name under metadata and servicePort is the port under the ports section).
</b></details>
<details>
<summary>What is Ingress Controller?</summary><br><b>
An implementation for Ingress. It's basically another pod (or set of pods) that does evaluates and processes Ingress rules and this it manages all the redirections.
There are multiple Ingress Controller implementations (the one from Kubernetes is Kubernetes Nginx Ingress Controller).
</b></details>
<details>
<summary>What are some use cases for using Ingress?</summary><br><b>
* Multiple sub-domains (multiple host entries, each with its own service)
* One domain with multiple services (multiple paths where each one is mapped to a different service/application)
</b></details>
<details>
<summary>How to list Ingress in your namespace?</summary><br><b>
kubectl get ingress
</b></details>
<details>
<summary>What is Ingress Default Backend?</summary><br><b>
It specifies what do with an incoming request to the Kubernetes cluster that isn't mapped to any backend (= no rule to for mapping the request to a service). If the default backend service isn't defined, it's recommended to define so users still see some kind of message instead of nothing or unclear error.
</b></details>
<details>
<summary>How to configure a default backend?</summary><br><b>
Create Service resource that specifies the name of the default backend as reflected in `kubectl desrcibe ingress ...` and the port under the ports section.
</b></details>
<details>
<summary>How to configure TLS with Ingress?</summary><br><b>
Add tls and secretName entries.
```
spec:
tls:
- hosts:
- some_app.com
secretName: someapp-secret-tls
````
</b></details>
<details>
<summary>True or False? When configuring Ingress with TLS, the Secret component must be in the same namespace as the Ingress component</summary><br><b>
[kubernetes.io](https://kubernetes.io/docs/concepts/services-networking/network-policies): "NetworkPolicies are an application-centric construct which allow you to specify how a pod is allowed to communicate with various network "entities"..."
In simpler words, Network Policies specify how pods are allowed/disallowed to communicate with each other and/or other network endpoints.
</b></details>
<details>
<summary>What are some use cases for using Network Policies?</summary><br><b>
- Security: You want to prevent from everyone to communicate with a certain pod for security reasons
- Controling network traffic: You would like to deny network flow between two specific nodes
</b></details>
<details>
<summary>True or False? If no network policies are applied to a pod, then no connections to or from it are allowed</summary><br><b>
False. By default pods are non-isolated.
</b></details>
<details>
<summary>In case of two pods, if there is an egress policy on the source denining traffic and ingress policy on the destination that allows traffic then, traffic will be allowed or denied?</summary><br><b>
Denied. Both source and destination policies has to allow traffic for it to be allowed.
Namespaces allow you split your cluster into virtual clusters where you can group your applications in a way that makes sense and is completely separated from the other groups (so you can for example create an app with the same name in two different namespaces)
<summary>Why to use namespaces? What is the problem with using one default namespace?</summary><br><b>
When using the default namespace alone, it becomes hard over time to get an overview of all the applications you manage in your cluster. Namespaces make it easier to organize the applications into groups that makes sense, like a namespace of all the monitoring applications and a namespace for all the security applications, etc.
Namespaces can also be useful for managing Blue/Green environments where each namespace can include a different version of an app and also share resources that are in other namespaces (namespaces like logging, monitoring, etc.).
Another use case for namespaces is one cluster, multiple teams. When multiple teams use the same cluster, they might end up stepping on each others toes. For example if they end up creating an app with the same name it means one of the teams overriden the app of the other team because there can't be too apps in Kubernetes with the same name (in the same namespace).
<summary>True or False? When a namespace is deleted all resources in that namespace are not deleted but moved to another default namespace</summary><br><b>
False. When a namespace is deleted, the resources in that namespace are deleted as well.
<summary>Let's say you have three namespaces: x, y and z. In x namespace you have a ConfigMap referencing service in z namespace. Can you reference the ConfigMap in x namespace from y namespace?</code></summary><br><b>
No, you would have to create separate namespace in y namespace.
<summary>You suspect one of the pods is having issues, what do you do?</summary><br><b>
Start by inspecting the pods status. we can use the command `kubectl get pods` (--all-namespaces for pods in system namespace)<br>
If we see "Error" status, we can keep debugging by running the command `kubectl describe pod [name]`. In case we still don't see anything useful we can try stern for log tailing.<br>
In case we find out there was a temporary issue with the pod or the system, we can try restarting the pod with the following `kubectl scale deployment [name] --replicas=0`<br>
Setting the replicas to 0 will shut down the process. Now start it with `kubectl scale deployment [name] --replicas=1`
"Operators are software extensions to Kubernetes that make use of custom resources to manage applications and their components. Operators follow Kubernetes principles, notably the control loop."
</b></details>
<details>
<summary>Why do we need Operators?</summary><br><b>
The process of managing stateful applications in Kubernetes isn't as straightforward as managing stateless applications where reaching the desired status and upgrades are both handled the same way for every replica. In stateful applications, upgrading each replica might require different handling due to the stateful nature of the app, each replica might be in a different status. As a result, we often need a human operator to manage stateful applications. Kubernetes Operator is suppose to assist with this.
It uses the control loop used by Kubernetes in general. It watches for changes in the application state. The difference is that is uses a custom control loop.
In additions.
In addition, it also makes use of CRD's (Custom Resources Definitions) so basically it extends Kubernetes API.
</b></details>
<details>
<summary>True or False? Kubernetes Operator used for stateful applications</summary><br><b>
1. Operator SDK - allows developers to build operators
2. Operator Lifecycle Manager - helps to install, update and generally manage the lifecycle of all operators
3. Operator Metering - Enables usage reporting for operators that provide specialized services
</b></details>
<details>
<summary>Describe in detail what is the Operator Lifecycle Manager</summary><br><b>
It's part of the Operator Framework, used for managing the lifecycle of operators. It basically extends Kubernetes so a user can use a declarative way to manage operators (installation, upgrade, ...).
A ReplicaSet's purpose is to maintain a stable set of replica Pods running at any given time. As such, it is often used to guarantee the availability of a specified number of identical Pods.
A ReplicaSet is defined with fields, including a selector that specifies how to identify Pods it can acquire, a number of replicas indicating how many Pods it should be maintaining, and a pod template specifying the data of new Pods it should create to meet the number of replicas criteria.
A ReplicaSet then fulfills its purpose by creating and deleting Pods as needed to reach the desired number. When a ReplicaSet needs to create new Pods, it uses its Pod template.
<summary>Explain what are "Service Accounts" and in which scenario would use create/use one</summary><br><b>
[Kubernetes.io](https://kubernetes.io/docs/tasks/configure-pod-container/configure-service-account): "A service account provides an identity for processes that run in a Pod."
An example of when to use one:
You define a pipeline that needs to build and push an image. In order to have sufficient permissions to build an push an image, that pipeline would require a service account with sufficient permissions.
</b></details>
<details>
<summary>What happens you create a pod and you DON'T specify a service account?</summary><br><b>
The pod is automatically assigned with the default service account (in the namespace where the pod is running).
</b></details>
<details>
<summary>Explain how Service Accounts are different from User Accounts</summary><br><b>
- User accounts are global while Service accounts unique per namespace
- User accounts are meant for humans or client processes while Service accounts are for processes which run in pods
</b></details>
<details>
<summary>How to list Service Accounts?</summary><br><b>
<summary>You have one Kubernetes cluster and multiple teams that would like to use it. You would like to limit the resources each team consumes in the cluster. Which Kubernetes concept would you use for that?</summary><br><b>
Namespaces will allow to limit resources and also make sure there are no collisions between teams when working in the cluster (like creating an app with the same name).
</b></details>
<details>
<summary>What Kube Proxy does?</summary><br><b>
</b></details>
<details>
<summary>What "Resources Quotas" are used for and how?</summary><br><b>
</b></details>
<details>
<summary>Explain ConfigMap</summary><br><b>
Separate configuration from pods.
It's good for cases where you might need to change configuration at some point but you don't want to restart the application or rebuild the image so you create a ConfigMap and connect it to a pod but externally to the pod.
Overall it's good for:
* Sharing the same configuration between different pods
* Storing external to the pod configuration
</b></details>
<details>
<summary>How to use ConfigMaps?</summary><br><b>
1. Create it (from key&value, a file or an env file)
2. Attach it. Mount a configmap as a volume
</b></details>
<details>
<summary>Trur or False? Sensitive data, like credentials, should be stored in a ConfigMap</summary><br><b>
False. Use secret.
</b></details>
<details>
<summary>Explain "Horizontal Pod Autoscaler"</summary><br><b>
Scale the number of pods automatically on observed CPU utilization.
</b></details>
<details>
<summary>When you delete a pod, is it deleted instantly? (a moment after running the command)</summary><br><b>
</b></details>
<details>
<summary>How to delete a pod instantly?</summary><br><b>
Use "--grace-period=0 --force"
</b></details>
<details>
<summary>Explain Liveness probe</summary><br><b>
</b></details>
<details>
<summary>Explain Readiness probe</summary><br><b>
</b></details>
<details>
<summary>What does being cloud-native mean?</summary><br><b>
</b></details>
<details>
<summary>Explain the pet and cattle approach of infrastructure with respect to kubernetes</summary><br><b>
</b></details>
<details>
<summary>Describe how you one proceeds to run a containerised web app in K8s, which should be reachable from a public URL.</summary><br><b>
</b></details>
<details>
<summary>How would you troubleshoot your cluster if some applications are not reachable any more?</summary><br><b>
</b></details>
<details>
<summary>Describe what CustomResourceDefinitions there are in the Kubernetes world? What they can be used for?</summary><br><b>
</b></details>
<details>
<summary> How does scheduling work in kubernetes?</summary><br><b>
The control plane component kube-scheduler asks the following questions,
1. What to schedule? It tries to understand the pod-definition specifications
2. Which node to schedule? It tries to determine the best node with available resources to spin a pod
3. Binds the Pod to a given node
View more [here](https://www.youtube.com/watch?v=rDCWxkvPlAw)
</b></details>
<details>
<summary> How are labels and selectors used?</summary><br><b>
Sometimes when you would like to deploy a certain application to your cluster, you need to create multiple YAML files/components like: Secret, Service, ConfigMap, etc. This can be tedious task. So it would make sense to ease the process by introducing something that will allow us to share these bundle of YAMLs every time we would like to add an application to our cluster. This something is called Helm.
A common scenario is having multiple Kubernetes clusters (prod, dev, staging). Instead of individually applying different YAMLs in each cluster, it makes more sense to create one Chart and install it in every cluster.
Helm Charts is a bundle of YAML files. A bundle that you can consume from repositories or create your own and publish it to the repositories.
</b></details>
<details>
<summary>It is said that Helm is also Templating Engine. What does it mean?</summary><br><b>
It is useful for scenarios where you have multiple applications and all are similar, so there are minor differences in their configuration files and most values are the same. With Helm you can define a common blueprint for all of them and the values that are not fixed and change can be placeholders. This is called a template file and it looks similar to the following
```
apiVersion: v1
kind: Pod
metadata:
name: {[ .Values.name ]}
spec:
containers:
- name: {{ .Values.container.name }}
image: {{ .Values.container.image }}
port: {{ .Values.container.port }}
```
The values themselves will in separate file:
```
name: some-app
container:
name: some-app-container
image: some-app-image
port: 1991
```
</b></details>
<details>
<summary>What are some use cases for using Helm template file?</summary><br><b>
* Deploy the same application across multiple different environments
* CI/CD
</b></details>
<details>
<summary>Explain the Helm Chart Directory Structure</summary><br><b>
someChart/ -> the name of the chart
Chart.yaml -> meta information on the chart
values.yaml -> values for template files
charts/ -> chart dependencies
templates/ -> templates files :)
</b></details>
<details>
<summary>How do you search for charts?</summary><br><b>
Helm allows you to upgrade, remove and rollback to previous versions of charts. In version 2 of Helm it was with what is known as "Tiller". In version 3, it was removed due to security concerns.
<summary>Explain expressions and statements</summary><br><b>
An expression is anything that results in a value (even if the value is None). Basically, any sequence of literals so, you can say that a string, integer, list, ... are all expressions.
Statements are instructions executed by the interpreter like variable assignments, for loops and conditionals (if-else).
* Make it easier to extend the functionality of the system
* Make the code more readable and easier to maintain
SOLID is:
* Single Responsibility - A class should only have a single responsibility
* Open-Closed - An entity should be open for extension, but closed for modification. What this practically means is that you should extend functionality by adding a new code and not by modifying it. Your system should be separated into components so it can be easily extended without breaking everything.
* Liskov Substitution - Any derived class should be able to substitute the its parent without altering its corrections. Practically, every part of the code will get the expected result no matter which part is using it
It's a search algorithm used with sorted arrays/lists to find a target value by dividing the array each iteration and comparing the middle value to the target value. If the middle value is smaller than target value, then the target value is searched in the right part of the divided array, else in the left side. This continues until the value is found (or the array divided max times)
<summary>Describe what would be the time complexity of the operations <code>access</code>, <code>search</code><code>insert</code> and <code>remove</code> for the following data structures:</summary><br><b>
* Stack
* Queue
* Linked List
* Binary Search Tree
</b></details>
<details>
<summary>What is the complexity for the best, worst and average cases of each of the following algorithms?:
<summary>Describe (no need to implement) how to detect a loop in a Linked List</summary><br><b>
There are multiple ways to detect a loop in a linked list. I'll mention three here:
Worst solution:<br>
Two pointers where one points to the head and one points to the last node. Each time you advance the last pointer by one and check whether the distance between head pointer to the moved pointer is bigger than the last time you measured the same distance (if not, you have a loop).<br>
The reason it's probably the worst solution, is because time complexity here is O(n^2)
Decent solution:<br>
Create an hash table and start traversing the linked list. Every time you move, check whether the node you moved to is in the hash table. If it isn't, insert it to the hash table. If you do find at any point the node in the hash table, it means you have a loop. When you reach None/Null, it's the end and you can return "no loop" value.
This one is very easy to implement (just create a hash table, update it and check whether the node is in the hash table every time you move to the next node) but since the auxiliary space is O(n) because you create a hash table then, it's not the best solution
Good solution:<br>
Instead of creating a hash table to document which nodes in the linked list you have visited, as in the previous solution, you can modify the Linked List (or the Node to be precise) to have a "visited" attribute. Every time you visit a node, you set "visited" to True.<br>
Time compleixty is O(n) and Auxiliary space is O(1), so it's a good solution but the only problem, is that you have to modify the Linked List.
Best solution:<br>
You set two pointers to traverse the linked list from the beginning. You move one pointer by one each time and the other pointer by two. If at any point they meet, you have a loop. This solution is also called "Floyd's Cycle-Finding"<br>
Time complexity is O(n) and auxiliary space is O(1). Perfect :)
<summary>Name 3 design patterns. Do you know how to implement (= provide an example) these design pattern in any language you'll choose?</summary><br><b>
| Identify the data type | Data Types | [Exercise](exercises/python/data_types.md) | [Solution](exercises/python/solutions/data_types_solution.md)
| Identify the data type - Advanced | Data Types | [Exercise](exercises/python/advanced_data_types.md) | [Solution](exercises/python/solutions/advanced_data_types_solution.md)
<summary>In Python, functions are first-class objects. What does it mean?</summary><br><b>
In general, first class objects in programming languages are objects which can be assigned to variable, used as a return value and can be used as arguments or parameters.<br>
In python you can treat functions this way. Let's say we have the following function
```
def my_function():
return 5
```
You can then assign a function to a variables like this `x = my_function` or you can return functions as return values like this `return my_function`
For more details about errors and exceptions follow this [https://docs.python.org/3/tutorial/errors.html](https://docs.python.org/3/tutorial/errors.html)
<summary>What _ is used for in Python?</summary><br><b>
1. Translation lookup in i18n
2. Hold the result of the last executed expression or statement in the interactive interpreter.
3. As a general purpose "throwaway" variable name. For example: x, y, _ = get_data() (x and y are used but since we don't care about third variable, we "threw it away").
A <code>lambda</code> expression is an 'anonymous' function, the difference from a normal defined function using the keyword `def`` is the syntax and usage.
Generally it is considered a bad practice under PEP 8 to assign a lambda expresion, they are meant to be used as parameters and inside of other defined functions.
First you ask the user for the amount of numbers that will be use. Use a while loop that runs until amount_of_numbers becomes 0 through subtracting amount_of_numbers by one each loop. In the while loop you want ask the user for a number which will be added a variable each time the loop runs.
<summary>How to check if all the elements in a given lists are unique? so [1, 2, 3] is unique but [1, 1, 2, 3] is not unique because 1 exists twice</summary><br><b>
<summary>You have the following list: <code>[{'name': 'Mario', 'food': ['mushrooms', 'goombas']}, {'name': 'Luigi', 'food': ['mushrooms', 'turtles']}]</code>
Extract all type of foods. Final output should be: {'mushrooms', 'goombas', 'turtles'}</summary><br><b>
<summary>How do you join path components? for example <code>/home</code> and <code>luig</code> will result in <code>/home/luigi</code></summary><br><b>
</b></details>
<details>
<summary>How do you remove non-empty directory?</summary><br><b>
<summary>How to extract the unique characters from a string? for example given the input "itssssssameeeemarioooooo" the output will be "mrtisaoe"</summary><br><b>
```
x = "itssssssameeeemarioooooo"
y = ''.join(set(x))
```
</b></details>
<details>
<summary>Find all the permutations of a given string</summary><br><b>
<summary>What is the output of the following code: <code>"".join(["a", "h", "m", "a", "h", "a", "n", "q", "r", "l", "o", "i", "f", "o", "o"])[2::3]</code></summary><br><b>
<summary>You have the following list of nested lists: <code>[['Mario', 90], ['Geralt', 82], ['Gordon', 88]]</code> How to sort the list by the numbers in the nested lists?</code></summary><br><b>
<summary>What data types are you familiar with that are not Python built-in types but still provided by modules which are part of the standard library?</summary><br><b>
This is a good reference https://docs.python.org/3/library/datatypes.html
<summary>You wrote a class to represent a car. How would you compare two cars instances if two cars are equal if they have the same model and color?</summary><br><b>
<summary>You have created a web page where a user can upload a document. But the function which reads the uploaded files, runs for a long time, based on the document size and user has to wait for the read operation to complete before he/she can continue using the web site. How can you overcome this?</summary><br><b>
<summary>What is wrong with the old approach of watching for a specific value and trigger an email/phone alert while value is exceeded?</summary><br><b>
This approach require from a human to always check why the value exceeded and how to handle it while today, it is more effective to notify people only when they need to take an actual action.
If the issue doesn't require any human intervention, then the problem can be fixed by some processes running in the relevant environment.
The Git directory is where Git stores the meta data and object database for your project. This is the most important part of Git, and it is what is copied when you clone a repository from another computer.
The working directory is a single checkout of one version of the project. These files are pulled out of the compressed database in the Git directory and placed on disk for you to use or modify.
The staging area is a simple file, generally contained in your Git directory, that stores information about what will go into your next commit. It’s sometimes referred to as the index, but it’s becoming standard to refer to it as the staging area.
This answer taken from [git-scm.com](https://git-scm.com/book/en/v1/Getting-Started-Git-Basics#_the_three_states)
The <code>.git</code> folder contains all the information that is necessary for your project in version control and all the information about commits, remote repository address, etc. All of them are present in this folder. It also contains a log that stores your commit history so that you can roll back to history.
This info copied from [https://stackoverflow.com/questions/29217859/what-is-the-git-folder](https://stackoverflow.com/questions/29217859/what-is-the-git-folder)
<summary>Are you familiar with gitattributes? When would you use it?</summary><br><b>
gitattributes allow you to define attributes per pathname or path pattern.<br>
You can use it for example to control endlines in files. In Windows and Unix based systems, you have different characters for new lines (\r\n and \n accordingly). So using gitattributes we can align it for both Windows and Unix with `* text=auto` in .gitattributes for anyone working with git. This is way, if you use the Git project in Windows you'll get \r\n and if you are using Unix or Linux, you'll get \n.
With <code>var x int = 2</code> we are setting the variable type to integer while with <code>x := 2</code> we are letting Go figure out by itself the type.
Go's iota identifier is used in const declarations to simplify definitions of incrementing numbers. Because it can be used in expressions, it provides a generality beyond that of simple enumerations.
<br>
`x` and `y` in the first iota group, `z` in the second.
<br>
[Iota page in Go Wiki](https://github.com/golang/go/wiki/Iota)
<summary>What is better? Embedded documents or referenced?</summary><br><b>
</b></details>
<details>
<summary>Have you performed data retrieval optimizations in Mongo? If not, can you think about ways to optimize a slow data retrieval?</summary><br><b>
<summary>What are "Security Context Constraints"?</summary><br><b>
From [OpenShift Docs](https://docs.openshift.com/container-platform/4.7/authentication/managing-security-context-constraints.html): "Similar to the way that RBAC resources control user access, administrators can use security context constraints (SCCs) to control permissions for pods".
</b></details>
<details>
<summary>How to add the ability for the user `user1` to view the project `wonderland` assuming you are authorized to do so</summary><br><b>
* We are delivering the scripts to customers who don't have access to the public network and don't necessarily have Ansible installed on their systems.
<summary>Which of the following queries would you use?
```
SELECT count(*) SELECT count(*)
FROM shawarma_purchases FROM shawarma_purchases
WHERE vs. WHERE
YEAR(purchased_at) == '2017' purchased_at >= '2017-01-01' AND
purchased_at <= '2017-31-12'
```
</summary><br><b>
```
SELECT count(*)
FROM shawarma_purchases
WHERE
purchased_at >= '2017-01-01' AND
purchased_at <= '2017-31-12'
```
When you use a function (`YEAR(purchased_at)`) it has to scan the whole database as opposed to using indexes and basically the column as it is, in its natural state.
An availability set is a logical grouping of VMs that allows Azure to understand how your application is built to provide redundancy and availability. It is recommended that two or more VMs are created within an availability set to provide for a highly available application and to meet the 99.95% Azure SLA.
<summary>What is the Azure Security Center? What are some of its features?</summary><br><b>
It's a monitoring service that provides threat protection across all of the services in Azure.
More specifically, it:
* Provides security recommendations based on your usage
* Monitors security settings and continuously all the services
* Analyzes and identifies potential inbound attacks
* Detects and blocks malware using machine learning
</b></details>
<details>
<summary>What is Azure Active Directory?</summary><br><b>
Azure AD is a cloud-based identity service. You can use it as a standalone service or integrate it with existing Active Directory service you already running.
It is a set of tools to help developers write, run and debug GCP kubernetes based applications. It provides built-in support for rapid iteration, debugging and running applications in development and production K8s environments.
<summary>Can you deploy Anthos on AWS?</summary><br><b>
* Yes, Anthos on AWS is now GA. For more read [here](https://cloud.google.com/anthos/gke/docs/aws)
</b></details>
<details>
<summary>List and explain the enterprise security capabilities provided by Anthos</summary><br><b>
* Control plane security - GCP manages and maintains the K8s control plane out of the box. The user can secure the api-server by using master authorized networks and private clusters. These allow the user to disable access on the public IP address by assigning a private IP address to the master.
* Node security - By default workloads are provisioned on Compute engine instances that use Google's Container Optimised OS. This operating system implements a locked-down firewall, limited user accounts with root disabled and a read-only filesystem. There is a further option to enable GKE Sandbox for stronger isolation in multi-tenant deployment scenarios.
* Network security - Within a created cluster VPC, Anthos GKE leverages a powerful software-defined network that enables simple Pod-to-Pod communications. Network policies allow locking down ingress and egress connections in a given namespace. Filtering can also be implemented to incoming load-balanced traffic for services that require external access, by supplying whitelisted CIDR IP ranges.
* Workload security - Running workloads run with limited privileges, default Docker AppArmor security policies are applied to all Kubernetes Pods. Workload identity for Anthos GKE aligns with the open source kubernetes service accounts with GCP service account permissions.
<summary>How can workloads deployed on Anthos GKE on-prem clusters securely connect to Google Cloud services?</summary><br><b>
* Google Cloud Virtual Private Network (Cloud VPN) - this is for secure networking
* Google Cloud Key Management Service (Cloud KMS) - for key management
</b></details>
<details>
<summary>What is Island Mode configuration with regards to networking in Anthos GKE deployed on-prem?</summary><br><b>
* This is when pods can directly talk to each other within a cluster, but cannot be reached from outside the cluster thus forming an "island" within the network that is not connected to the external network.
It is a core component of the Anthos stack which provides platform, service and security operators with a single, unified approach to multi-cluster management that spans both on-premises and cloud environments. It closely follows K8s best practices, favoring declarative approaches over imperative operations, and actively monitors cluster state and applies the desired state as defined in Git. It includes three key components as follows:
1. An importer that reads from a central Git repository
2. A component that synchronises stored configuration data into K8s objects
It follows common modern software development practices which makes cluster configuration, management and policy changes auditable, revertable, and versionable easily enforcing IT governance and unifying resource management in an organisation.
* It is a suite of tools that assist in monitoring and managing deployed services on Anthos of all shapes and sizes whether running in cloud, hybrid or multi-cloud environments. It leverages the APIs and core components from Istio, a highly configurable and open-source service mesh platform.
<summary>Describe the two main components of Anthos Service Mesh</summary><br><b>
1. Data plane - it consists of a set of distributed proxies that mediate all inbound and outbound network traffic between individual services which are configured using a centralised control plane and an open API
2. Control plane - is a fully managed offering outside of Anthos GKE clusters to simplify management overhead and ensure highest possible availability.
</b></details>
<details>
<summary>What are the components of the managed control plane of Anthos Service Mesh?</summary><br><b>
1. Traffic Director - it is GCP's fully managed service mesh traffic control plane, responsible for translating Istio API objects into configuration information for the distributed proxies, as well as directing service mesh ingress and egress traffic
2. Managed CA - is a centralised certificate authority responsible for providing SSL certificates to each of the distributed proxies, authentication information and distributing secrets
3. Operations tooling - formerly stackdriver, provides a managed ingestion point for observability and telemetry, specifically monitoring, tracing and logging data generated by each of the proxies. This powers the observability dashboard for operators to visually inspect their services and service dependencies assisting in the implementation of SRE best practices for monitoring SLIs and establishing SLOs.
<summary>How does Anthos Service Mesh help?</summary><br><b>
Tool and technology integration that makes up Anthos service mesh delivers signficant operational benefits to Anthos environments, with minimal additional overhead such as follows:
* Uniform observability - the data plane reports service to service communication back to the control plane generating a service dependency graph. Traffic inspection by the proxy inserts headers to facilitate distributed tracing, capturing and reporting service logs together with service-level metrics (i.e latency, errors, availability).
* Policy-driven security - policies can be enforced consistently across diverse protocols and runtimes as service communications are secured by default.
It is part of the Anthos stack that brings a serverless container experience to Anthos, offering a high-level platform experience on top of K8s clusters. It is built with Knative, an open-source operator for K8s that brings serverless application serving and eventing capabilities.
<summary>How does Cloud Run for Anthos simplify operations?</summary><br><b>
Platform teams in organisations that wish to offer developers additional tools to test, deploy and run applications can use Knative to enhance this experience on Anthos as Cloud Run. Below are some of the benefits;
* Easy migration from K8s deployments - Without Cloud Run, platform engineers have to configure deployment, service, and HorizontalPodAutoscalers(HPA) objects to a loadbalancer and autoscaling. If application is already serving traffic it becomes hard to change configurations or roll back efficiently. Using Cloud Run all this is managed thus the Knative service manifest describes the application to be autoscaled and loadbalanced
* Autoscaling - a sudden traffic spike may cause application containers in K8s to crash due to overload thus an efficient automated autoscaling is executed to serve the high volume of traffic
* Networking - it has built-in load balancing capabilities and policies for traffic splitting between multiple versions of an application.
* Releases and rollouts - supports the notion of the Knatibe API's revisions which describe new versions or different configurations of your application and canary deployments by splitting traffic.
* Monitoring - observing and recording metrics such as latency, error rate and requests per second.
<summary>List and explain three high-level out of the box autoscaling primitives offered by Cloud Run for Anthos that do not exist in K8s natively</summary><br><b>
* Rapid, request-based autoscaling - default autoscalers monitor request metrics which allows Cloud Run for Anthos to handle spiky traffic patterns smoothly
* Concurrency controls - limits such as max in-flight requests per container are enforced to ensure the container does not become overloaded and crash. More containers are added to handle the spiky traffic, buffering the requests.
* Scale to zero - if an application is inactive for a while Cloud Run scales it down to zero to reduce its footprint. Alternatively one can turn off scale-to-zero to prevent cold starts.
* Management Network - used for internal communication between OpenStack components. Any IP address in this network is accessible only within the datacetner
* Guest Network - used for communication between instances/VMs
* API Network - used for services API communication. Any IP address in this network is publicly accessible
* External Network - used for public communication. Any IP address in this network is accessible by anyone on the internet
* glance-api - responsible for handling image API calls such as retrieval and storage. It consists of two APIs: 1. registry-api - responsible for internal requests 2. user API - can be accessed publicly
* glance-registry - responsible for handling image metadata requests (e.g. size, type, etc). This component is private which means it's not available publicly
* metadata definition service - API for custom metadata
* database - for storing images metadata
* image repository - for storing images. This can be a filesystem, swift object storage, HTTP, etc.
</b></details>
#### OpenStack - Swift
<details>
<summary>Explain Swift in detail</summary><br><b>
* Swift is Object Store service and is an highly available, distributed and consistent store designed for storing a lot of data
* Swift is distributing data across multiple servers while writing it to multiple disks
* One can choose to add additional servers to scale the cluster. All while swift maintaining integrity of the information and data replications.
</b></details>
<details>
<summary>Can users store by default an object of 100GB in size?</summary><br><b>
Not by default. Object Storage API limits the maximum to 5GB per object but it can be adjusted.
</b></details>
<details>
<summary>Explain the following in regards to Swift:
<summary>Explain Cinder in detail</summary><br><b>
* Cinder is OpenStack Block Storage service
* It basically provides used with storage resources they can consume with other services such as Nova
* One of the most used implementations of storage supported by Cinder is LVM
* From user perspective this is transparent which means the user doesn't know where, behind the scenes, the storage is located or what type of storage is used
<summary>What the "Zero Trust" concept means? How Organizations deal with it?</summary><br><b>
[Codefresh definition](https://codefresh.io/security-testing/codefresh-runner-overview): "Zero trust is a security concept that is centered around the idea that organizations should never trust anyone or anything that does not originate from their domains. Organizations seeking zero trust automatically assume that any external services it commissions have security breaches and may leak sensitive information"
SSO (Single Sign-on), is a method of access control that enables a user to log in once and gain access to the resources of multiple software systems without being prompted to log in again.
Multi-Factor Authentication (Also known as 2FA). Allows the user to present two pieces of evidence, credentials, when logging into an account.
- The credentials fall into any of these three categories: something you know (like a password or PIN), something you have (like a smart card), or something you are (like your fingerprint). Credentials must come from two different categories to enhance security.
Access control based on user roles (i.e., a collection of access authorizations a user receives based on an explicit or implicit assumption of a given role). Role permissions may be inherited through a role hierarchy and typically reflect the permissions needed to perform defined functions within an organization. A given role may apply to a single individual or to several individuals.
- RBAC mapped to job function, assumes that a person will take on different roles, overtime, within an organization and different responsibilities in relation to IT systems.
<summary>What is SSH how does it work?</summary><br><b>
[Wikipedia Definition](https://en.wikipedia.org/wiki/SSH_(Secure_Shell)): "SSH or Secure Shell is a cryptographic network protocol for operating network services securely over an unsecured network."
[Hostinger.com Definition](https://www.hostinger.com/tutorials/ssh-tutorial-how-does-ssh-work): "SSH, or Secure Shell, is a remote administration protocol that allows users to control and modify their remote servers over the Internet."
[This site](https://www.hostinger.com/tutorials/ssh-tutorial-how-does-ssh-work) explains it in a good way.
A asymmetric encryption is any technique where the there is two different keys that are used for encryption and decryption, these keys are known as public key and private key.
<summary>What is "Key Exchange" (or "key establishment") in cryptography?</summary><br><b>
[Wikipedia](https://en.wikipedia.org/wiki/Key_exchange): "Key exchange (also key establishment) is a method in cryptography by which cryptographic keys are exchanged between two parties, allowing use of a cryptographic algorithm."
</b></details>
<details>
<summary>True or False? The symmetrical encryption is making use of public and private keys where the private key is used to decrypt the data encrypted with a public key</summary><br><b>
False. This description fits the asymmetrical encryption.
</b></details>
<details>
<summary>True or False? The private key can be mathematically computed from a public key</summary><br><b>
Cross Site Scripting (XSS) is an type of a attack when the attacker inserts browser executable code within a HTTP response. Now the injected attack is not stored in the web application, it will only affact the users who open the maliciously crafted link or third-party web page. A successful attack allows the attacker to access any cookies, session tokens, or other sensitive information retained by the browser and used with that site
You can test by detecting user-defined variables and how to input them. This includes hidden or non-obvious inputs such as HTTP parameters, POST data, hidden form field values, and predefined radio or selection values. You then analyze each found vector to see if their are potential vulnerabilities, then when found you craft input data with each input vector. Then you test the crafted input and see if it works.
SQL injection is an attack consists of inserts either a partial or full SQL query through data input from the browser to the web application. When a successful SQL injection happens it will allow the attacker to read sensitive information stored on the database for the web application.
You can test by using a stored procedure, so the application must be sanitize the user input to get rid of the tisk of code injection. If not then the user could enter bad SQL, that will then be executed within the procedure
DNS spoofing occurs when a particular DNS server’s records of “spoofed” or altered maliciously to redirect traffic to the attacker. This redirection of traffic allows the attacker to spread malware, steal data, etc.
- Use encrypted data transfer protocols - Using end-to-end encryption vian SSL/TLS will help decrease the chance that a website / its visitors are compromised by DNS spoofing.
- Use DNSSEC - DNSSEC, or Domain Name System Security Extensions, uses digitally signed DNS records to help determine data authenticity.
- Implement DNS spoofing detection mechanisms - it’s important to implement DNS spoofing detection software. Products such as XArp help product against ARP cache poisoning by inspecting the data that comes through before transmitting it.
Stuxnet is a computer worm that was originally aimed at Iran’s nuclear facilities and has since mutated and spread to other industrial and energy-producing facilities. The original Stuxnet malware attack targeted the programmable logic controllers (PLCs) used to automate machine processes. It generated a flurry of media attention after it was discovered in 2010 because it was the first known virus to be capable of crippling hardware and because it appeared to have been created by the U.S. National Security Agency, the CIA, and Israeli intelligence.
Spectre is an attack method which allows a hacker to “read over the shoulder” of a program it does not have access to. Using code, the hacker forces the program to pull up its encryption key allowing full access to the program
Cross-Site Request Forgery (CSRF) is an attack that makes the end user to initate a unwanted action on the web application in which the user has a authenticated session, the attacker may user an email and force the end user to click on the link and that then execute malicious actions. When an CSRF attack is successful it will compromise the end user data
You can use OWASP ZAP to analyze a "request", and if it appears that there no protection against cross-site request forgery when the Security Level is set to 0 (the value of csrf-token is SecurityIsDisabled.) One can use data from this request to prepare a CSRF attack by using OWASP ZAP
HTTP Header Injection vulnerabilities occur when user input is insecurely included within server responses headers. If an attacker can inject newline characters into the header, then they can inject new HTTP headers and also, by injecting an empty line, break out of the headers into the message body and write arbitrary content into the application's response.
A buffer overflow (or buffer overrun) occurs when the volume of data exceeds the storage capacity of the memory buffer. As a result, the program attempting to write the data to the buffer overwrites adjacent memory locations.
MAC address flooding attack (CAM table flooding attack) is a type of network attack where an attacker connected to a switch port floods the switch interface with very large number of Ethernet frames with different fake source MAC address.
CPDoS or Cache Poisoned Denial of Service. It poisons the CDN cache. By manipulating certain header requests, the attacker forces the origin server to return a Bad Request error which is stored in the CDN’s cache. Thus, every request that comes after the attack will get an error page.
Elasticserach, Logstash and Kibana are also known as the ELK stack.
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<summary>Explain what is Elasticsearch</summary><br><b>
From the official [docs](https://www.elastic.co/guide/en/elasticsearch/reference/current/documents-indices.html):
"Elasticsearch is a distributed document store. Instead of storing information as rows of columnar data, Elasticsearch stores complex data structures that have been serialized as JSON documents"
"Kibana is an open source analytics and visualization platform designed to work with Elasticsearch. You use Kibana to search, view, and interact with data stored in Elasticsearch indices. You can easily perform advanced data analysis and visualize your data in a variety of charts, tables, and maps."
<summary>Describe what happens from the moment an app logged some information until it's displayed to the user in a dashboard when the Elastic stack is used</summary><br><b>
* Track the status of all the nodes in the cluster
* Verify replicas are working and the data is available from every data node.
* No hot nodes (no data node that works much harder than other nodes)
While there can be multiple master nodes in reality only of them is the elected master node.
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<summary>What is an ingest node?</summary><br><b>
A node which responsible for parsing the data. In case you don't use logstash then this node can recieve data from beats and parse it, similarly to how it can be parsed in Logstash.
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<summary>What is Coordinating node?</summary><br><b>
A Coordinating node responsible for routing requests out and in to the cluser (data nodes).
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<summary>How data is stored in elasticsearch?</summary><br><b>
* Data is stored in an index
* The index is spread across the cluster using shards
Index in Elastic is in most cases compared to a whole database from the SQL/NoSQL world.<br>
You can choose to have one index to hold all the data of your app or have multiple indices where each index holds different type of your app (e.g. index for each service your app is running).
The official docs also offer a great explanation (in general, it's really good documentation, as every project should have):
"An index can be thought of as an optimized collection of documents and each document is a collection of fields, which are the key-value pairs that contain your data"
An index is split into shards and documents are hashed to a particular shard. Each shard may be on a different node in a cluster and each one of the shards is a self contained index.<br>
This allows Elasticsearch to scale to an entire cluster of servers.
Continuing with the comparison to SQL/NoSQL a Document in Elastic is a row in table in the case of SQL or a document in a collection in the case of NoSQL.
As in NoSQL a Document is a JSON object which holds data on a unit in your app. What is this unit depends on the your app. If your app related to book then each document describes a book. If you are app is about shirts then each document is a shirt.
<summary>You check the health of your elasticsearch cluster and it's red. What does it mean? What can cause the status to be yellow instead of green?</summary><br><b>
Red means some data is unavailable.
Yellow can be caused by running single node cluster instead of multi-node.
<summary>True or False? Elasticsearch indexes all data in every field and each indexed field has the same data structure for unified and quick query ability</summary><br><b>
False.
From the official docs:
"Each indexed field has a dedicated, optimized data structure. For example, text fields are stored in inverted indices, and numeric and geo fields are stored in BKD trees."
In a network/cloud environment where failures can be expected any time, it is very useful and highly recommended to have a failover mechanism in case a shard/node somehow goes offline or disappears for whatever reason.
To this end, Elasticsearch allows you to make one or more copies of your index’s shards into what are called replica shards, or replicas for short.
<summary>Can you explain Term Frequency & Document Frequency?</summary><br><b>
Term Frequency is how often a term appears in a given document and Document Frequency is how often a term appears in all documents. They both are used for determining the relevance of a term by calculating Term Frequency / Document Frequency.
<summary>What this command does? <code>curl -X PUT "localhost:9200/customer/_doc/1?pretty" -H 'Content-Type: application/json' -d'{ "name": "John Doe" }'</code></summary><br><b>
It creates customer index if it doesn't exists and adds a new document with the field name which is set to "John Dow". Also, if it's the first document it will get the ID 1.
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<summary>What will happen if you run the previous command twice? What about running it 100 times?</code></summary><br><b>
1. If name value was different then it would update "name" to the new value
2. In any case, it bumps version field by one
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<summary>What is the Bulk API? What would you use it for?</code></summary><br><b>
Bulk API is used when you need to index multiple documents. For high number of documents it would be significantly faster to use rather than individual requests since there are less network roundtrips.
<summary>Explain what is Relevance Score</summary><br><b>
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<summary>Explain Query Context and Filter Context</summary><br><b>
From the official docs:
"In the query context, a query clause answers the question “How well does this document match this query clause?” Besides deciding whether or not the document matches, the query clause also calculates a relevance score in the _score meta-field."
"In a filter context, a query clause answers the question “Does this document match this query clause?” The answer is a simple Yes or No — no scores are calculated. Filter context is mostly used for filtering structured data"
<summary>Describe how would an architecture of production environment with large amounts of data would be different from a small-scale environment</summary><br><b>
There are several possible answers for this question. One of them is as follows:
A small-scale architecture of elastic will consist of the elastic stack as it is. This means we will have beats, logstash, elastcsearch and kibana.<br>
A production environment with large amounts of data can include some kind of buffering component (e.g. Reddis or RabbitMQ) and also security component such as Nginx.
<summary>What is DNS? What is it used for?</summary><br><b>
DNS (Domain Name Systems) is a protocol used for converting domain names into IP addresses.<br>
As you know computer networking is done with IP addresses (layer 3 of the OSI model) but for as humans it's hard to remember IP addresses, it's much easier to remember names. This why we need something such as DNS to convert any domain name we type into an IP address. You can think on DNS as a huge phonebook or database where each corresponding name has an IP.
* The user types an address in the web browser (some_site.com)
* The operating system gets a request from the browser to translate the address the user entered
* A query created to check a local entry of the address exists in the system. In case it doesn't, the request is forwarded to the DNS resolver
* The Resolver is a server, usually configured by your ISP when you connect to the internet, that responsible for resolving your query by contacting other DNS servers
* The Resolver contacts the root nameserver (aka as .)
* The root nameserver responds with the address of the relevant Top Level Domain DNS server (if your address ends with org then the org TLD)
* The Resolver then contacts the TLD DNS and TLD DNS responds with the IP address that matches the address the user typed in the browser
* The Resolver passes this information to the browser
"Many processes running on many machines...only message-passing via an unreliable network with variable delays, and the system may suffer from partial failures, unreliable clocks, and process pauses."
<summary>What is "Shared-Nothing" architecture?</summary><br><b>
It's an architecture in which data is and retrieved from a single, non-shared, source usually exclusively connected to one node as opposed to architectures where the request can get to one of many nodes and the data will be retrieved from one shared location (storage, memory, ...).
4. The browser sends an HTTP request to the server
5. The server sends an HTTP response back to the browser
6. The browser renders the response (e.g. HTML)
7. The browser then sends subsequent requests as needed to the server to get the embedded links, javascript, images in the HTML and then steps 3 to 5 are repeated.
<summary>Define or Explain what is an API</summary><br><b>
I like this definition from [here](https://blog.christianposta.com/microservices/api-gateways-are-going-through-an-identity-crisis):
"An explicitly and purposefully defined interface designed to be invoked over a network that enables software developers to get programmatic access to data and functionality within an organization in a controlled and comfortable way."
<summary>What is Automation? How it's related or different from Orchestration?</summary><br><b>
Automation is the act of automating tasks to reduce human intervention or interaction in regards to IT technology and systems.<br>
While automation focuses on a task level, Orchestration is the process of automating processes and/or workflows which consists of multiple tasks that usually across multiple systems.
<summary>When you publish a project, you usually publish it with a license. What types of licenses are you familiar with and which one do you prefer to use?</summary><br><b>
A load balancer accepts (or denies) incoming network traffic from a client, and based on some criteria (application related, network, etc.) it distributes those communications out to servers (at least one).
* Scalability - using a load balancer, you can possibly add more servers in the backend to handle more requests/traffic from the clients, as opposed to using one server.
* Redundancy - if one server in the backend dies, the load balancer will keep forwarding the traffic/requests to the second server so users won't even notice one of the servers in the backend is down.
<summary>What are the drawbacks of round robin algorithm in load balancing?</summary><br><b>
* A simple round robin algorithm knows nothing about the load and the spec of each server it forwards the requests to. It is possible, that multiple heavy workloads requests will get to the same server while other servers will got only lightweight requests which will result in one server doing most of the work, maybe even crashing at some point because it unable to handle all the heavy workloads requests by its own.
* Each request from the client creates a whole new session. This might be a problem for certain scenarios where you would like to perform multiple operations where the server has to know about the result of operation so basically, being sort of aware of the history it has with the client. In round robin, first request might hit server X, while second request might hit server Y and ask to continue processing the data that was processed on server X already.
<summary>Explain use case for connection draining?</summary><br><b>
To ensure that a Classic Load Balancer stops sending requests to instances that are de-registering or unhealthy, while keeping the existing connections open, use connection draining. This enables the load balancer to complete in-flight requests made to instances that are de-registering or unhealthy.
The maximum timeout value can be set between 1 and 3,600 seconds on both GCP and AWS.
<summary>Explain the differences between copyleft and permissive licenses</summary><br><b>
In Copyleft, any derivative work must use the same licensing while in permissive licensing there are no such condition. GPL-3 is an example of copyleft license while BSD is an example of permissive license.
These are not DevOps related questions as you probably noticed, but since they are part of the DevOps interview process I've decided it might be good to keep them
If you worked in this area for more than 5 years it's hard to imagine the answer would be no. It also doesn't have to be big service outage. Maybe you merged some code that broke a project or its tests. Simply focus on what you learned from such experience.
<summary>You have three important tasks scheduled for today. One is for your boss, second for a colleague who is also a friend, third is for a customer. All tasks are equally important. What do you do first?</summary><br><b>
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<summary>You have a colleague you don‘t get along with. Tell us some strategies how you create a good work relationship with them anyway.</summary><br><b>
Better answer: Every person has strengths and weaknesses. This is true also for colleagues I don't have good work relationship with and this is what helps me to create good work relationship with them. If I am able to highlight or recognize their strengths I'm able to focus mainly on that when communicating with them.
These are only a suggestion, use them carefully. Not every interviewer will be able to answer these (or happy to) which should be perhaps a red flag warning for your regarding working in such place but that's really up to you.
Not only this will tell you what is expected from you, it will also provide big hint on the type of work you are going to do in the first months of your job.
<summary>You find out your database became a bottleneck and users experience issues accessing data. How can you deal with such situation?</summary><br><b>
Not much information provided as to why it became a bottleneck and what is current architecture, so one general approach could be<br>
to reduce the load on your database by moving frequently-accessed data to in-memory structure.
<summary>What is a connection pool?</summary><br><b>
Connection Pool is a cache of database connections and the reason it's used is to avoid an overhead of establishing a connection for every query done to a database.
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<summary>What is a connection leak?</summary><br><b>
A connection leak is a situation where database connection isn't closed after being created and is no longer needed.
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<summary>What is Table Lock?</summary><br><b>
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<summary>Your database performs slowly than usual. More specifically, your queries are taking a lot of time. What would you do?</summary><br><b>
* Query for running queries and cancel the irrelevant queries
* Check for connection leaks (query for running connections and include their IP)
* Check for table locks and kill irrelevant locking sessions
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<summary>What is a Data Warehouse?</summary><br><b>
"A data warehouse is a subject-oriented, integrated, time-variant and non-volatile collection of data in support of organisation's decision-making process"
<summary>What is an index in a database?</summary><br><b>
A database index is a data structure that improves the speed of operations in a table. Indexes can be created using one or more columns, providing the basis for both rapid random lookups and efficient ordering of access to records.
The load on the producers or consumers may be high which will then cause them to hang or crash.<br>
Instead of working in "push mode", the consumers can pull tasks only when they are ready to handle them. It can be fixed by using a streaming platform like Kafka, Kinesis, etc. This platform will make sure to handle the high load/traffic and pass tasks/messages to consumers only when the ready to get them.
A central processing unit (CPU) performs basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions in the program. This contrasts with external components such as main memory and I/O circuitry, and specialized processors such as graphics processing units (GPUs).
RAM (Random Access Memory) is the hardware in a computing device where the operating system (OS), application programs and data in current use are kept so they can be quickly reached by the device's processor. RAM is the main memory in a computer. It is much faster to read from and write to than other kinds of storage, such as a hard disk drive (HDD), solid-state drive (SSD) or optical drive.
An embedded system is a computer system - a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts.
DataOps seeks to reduce the end-to-end cycle time of data analytics, from the origin of ideas to the literal creation of charts, graphs and models that create value.
DataOps combines Agile development, DevOps and statistical process controls and applies them to data analytics.
<summary>What is Data Architecture?</summary><br><b>
An answer from [talend.com](https://www.talend.com/resources/what-is-data-architecture):
"Data architecture is the process of standardizing how organizations collect, store, transform, distribute, and use data. The goal is to deliver relevant data to people who need it, when they need it, and help them make sense of it."
<summary>What is Packer? What is it used for?</summary><br><b>
In general, Packer automates machine images creation.
It allows you to focus on configuration prior to deployment while making the images. This allows you start the instances much faster in most cases.
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<summary>Packer follows a "configuration->deployment" model or "deployment->configuration"?</summary><br><b>
A configuration->deployment which has some advantages like:
1. Deployment Speed - you configure once prior to deployment instead of configuring every time you deploy. This allows you to start instances/services much quicker.
2. More immutable infrastructure - with configuration->deployment it's not likely to have very different deployments since most of the configuration is done prior to the deployment. Issues like dependencies errors are handled/discovered prior to deployment in this model.
If you are looking for a way to prepare for a certain exam this is the section for you. Here you'll find a list of certificates, each references to a separate file with focused questions that will help you to prepare to the exam. Good luck :)
Thanks to all of our amazing [contributors](https://github.com/bregman-arie/devops-exercises/graphs/contributors) who make it easy for everyone to learn new things :)
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