devops-exercises/README.md

# DevOps Interview Questions


:information_source:  This repository contains interview questions on various DevOps related topics

:bar_chart:  There are currently **230** questions

:warning:  You don't need to know how to answer all the questions in this repo. DevOps is not about knowing all :)

:exclamation:  Some questions are more for testing your own knowledge than actual valid interview questions

:exclamation:  For interviewers, I suggest focusing on 3 things: the resume of the candidate, scenario questions and technical concepts. Don't have an interview of only specific technical questions

:pencil:  You can add more questions & answers by submitting pull requests :)

****

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<center>
<table>
  <tr>
    <td align="center"><a href="#devops"><img src="images/devops.png" width="75px;" height="75px;" alt="DevOps" /><br /><b>DevOps</b></a><br /><sub><a href="#devops-beginner">Beginner :baby:</a></sub><br><sub><a href="#devops-advanced">Advanced :star:</a></sub></td>
    <td align="center"><a href="#jenkins"><img src="images/jenkins.png" width="75px;" height="85px;" alt="Jenkins"/><br /><b>Jenkins</b></a><br /><sub><a href="#jenkins-beginner">Beginner :baby:</a></sub><br><sub><a href="#jenkins-advanced">Advanced :star:</a></sub></td>
    <td align="center"><a href="#aws"><img src="images/aws.png" width="120px;" height="75px;" alt="AWS"/><br /><b>AWS</b></a><br /><sub><a href="#aws-beginner">Beginner :baby:</a></sub><br><sub></td>
    <td align="center"><a href="#Network"><img src="images/network.png" width="75x;" height="75px;" alt="Network"/><br /><b>Network</b></a><br /><sub><a href="#network-beginner">Beginner :baby:</a></sub><br><sub></td>
    <td align="center"><a href="#linux"><img src="images/linux.png" width="75x;" height="75px;" alt="Linux"/><br /><b>Linux</b></a><br /><sub><a href="#linux-beginner">Beginner :baby:</a></sub><br><sub><a href="#linux-advanced">Advanced :star:</a></sub></td>
    <td align="center"><a href="#ansible"><img src="images/ansible.png" width="75px;" height="75px;" alt="Ansible"/><br /><b>Ansible</b></a><br /><sub><a href="#ansible-beginner">Beginner :baby:</a></sub><br><sub></td>
    <td align="center"><a href="#terraform"><img src="images/terraform.png" width="75px;" height="75px;" alt="Terraform"/><br /><b>Terraform</b></a><br /><sub><a href="#terraform-beginner">Beginner :baby:</a></sub><br><sub></td>
    <td align="center"><a href="#docker"><img src="images/docker.png" width="75px;" height="75px;" alt="Docker"/><br /><b>Docker</b></a><br /><sub><a href="#docker-beginner">Beginner :baby:</a></sub><br><sub></td>
  </tr>
  <tr>
    <td align="center"><a href="#kubernetes"><img src="images/kubernetes.png" width="75px;" height="75px;" alt="kubernetes"/><br /><b>Kubernetes</b></a><br /><sub><a href="#kubernetes-beginner">Beginner :baby:</a></sub><br></td>
    <td align="center"><a href="#python"><img src="images/python.png" width="75px;" height="75px;" alt="Python"/><br /><b>Python</b></a><br /><sub><a href="#python-beginner">Beginner :baby:</a></sub><br><sub><a href="#python-advanced">Advanced :star:</a></sub></td>
    <td align="center"><a href="#prometheus"><img src="images/prometheus.png" width="75px;" height="75px;" alt="Prometheus"/><br /><b>Prometheus</b></a><br /><sub><a href="#prometheus-beginner">Beginner :baby:</a></sub><br></td>
    <td align="center"><a href="#git"><img src="images/git.png" width="75px;" height="75px;" alt="Git"/><br /><b>Git</b></a><br /><sub><a href="#git-beginner">Beginner :baby:</a></sub><br><sub><a href="#git-advanced">Advanced :star:</a></sub></td>
    <td align="center"><a href="#go"><img src="images/go.png" width="75px;" height="75px;" alt="Go"/><br /><b>Go</b></a><br /><sub><a href="#go-beginner">Beginner :baby:</a></sub><br><sub></td>
    <td align="center"><a href="#mongo"><img src="images/mongo.png" width="75px;" height="75px;" alt="Mongo"/><br /><b>Mongo</b></a><br /><sub><a href="#mongo-beginner">Beginner :baby:</a></sub><br><sub></td>
    <td align="center"><a href="#openshift"><img src="images/openshift.png" width="75px;" height="75px;" alt="OpenShift"/><br /><b>OpenShift</b></a><br /><sub><a href="#openshift-beginner">Beginner :baby:</a></sub><br><sub></td>
    <td align="center"><a href="#shell-scripting"><img src="images/bash.png" width="75px;" height="75px;" alt="Bash"/><br /><b>Shell Scripting</b></a><br /><sub><a href="#shell-scripting-beginner">Beginner :baby:</a></sub><br><sub><a href="#shell-scripting-advanced">Advanced :star:</a></sub></td>
  </tr>
</table>
</center>
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## DevOps

<a name="devops-beginner"></a>
#### :baby: Beginner

<details>
<summary>What is Continuous Integration?</summary><br><b>

A development practice where developers integrate code into a shared repository frequently. It can range from a couple of changes every day or 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.
</b></details>

<details>
<summary>What is Continuous Deployment?</summary><br><b>
</b></details>

<details>
<summary>What is Continuous Delivery?</summary><br><b>
</b></details>

<details>
<summary>What DevOps helps us to achieve?</summary><br><b>
</b></details>

<details>
<summary>What do you consider as best practices for CI/CD?</summary><br><b>
</b></details>

<details>
<summary>What are the anti-patterns of DevOps?</summary><br><b>
</b></details>

<details>
<summary>What systems and/or tools are you using for the following?:

  * CI/CD
  * Provisioning infrastructure
  * Configuration Management
  * Monitoring & alerting
  * Logging
  * Code review
  * Code coverage
  * Tests</summary><br><b>
  * CI/CD - Jenkins, Circle CI, Travis
  * Provisioning infrastructure - Terraform, CloudFormation
  * Configuration Management - Ansible, Puppet, Chef
  * Monitoring & alerting - Prometheus, Nagios
  * Logging - Logstash, Graylog, Fluentd
  * Code review - Gerrit, Review Board
  * Code coverage - Cobertura, Clover, JaCoCo
  * Tests - Robot, Serenity, Gauge
</b></details>

<details>
<summary>What are you taking into consideration when choosing a tool/technology?</summary><br><b>

You may use one or all of the following:
  * mature vs. cutting edge
  * community size
  * architecture aspects - agent vs. agentless, master vs. masterless, etc.
</b></details>

<details>
<summary>What is the difference between SQL and NoSQL?</summary><br><b>
</b></details>

<details>
<summary>What the difference between VPN and VPS?</summary><br><b>
</b></details>

<details>
<summary>What is the difference between SSH and SSL?</summary><br><b>
</b></details>

<details>
<summary>What scripting language are you familiar with? why specifically this one?</summary><br><b>
</b></details>

<details>
<summary>How long do you think it would take you to learn another language?</summary><br><b>
</b></details>

<details>
<summary>Explain mutable vs. immutable infrastructure</summary><br><b>

In mutable infrastructure paradigm, changes applied on top of the existing infrastructure and over time
the infrastructure builds up a history of changes. Ansible, Puppet and Chef are examples to tools which
follow mutable infrastructure paradigm.

In immutable infrastructure paradigm, every change is actually new infrastructure. So a change
to a server will result in a new server instead of updating it. Terraform is an example of technology
which follows the immutable infrastructure paradigm.
</b></details>

<details>
<summary>What ways are you familiar with to deliver a software?</summary><br><b>

  * Archive - collect all your app files into one archive (e.g. tar) and deliver it to the user.
  * 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
  * Images - Either VM or container images where your package is included with everything it needs in order to run successfully.
</b></details>

<details>
<summary>What is caching? How it works? Why is it important?</summary><br><b>
</b></details>

<details>
<summary>Explain stateless vs. stateful</summary><br><b>
</b></details>

<details>
<summary>What is HTTP and how it works?</summary><br><b>
</b></details>

<details>
<summary>Describe the workflow of setting up some type of web server (Apache, IIS, Tomact, ...)</summary><br><b>
</b></details>

<details>
<summary>Explain monitoring. What is it? Why it's important?</summary><br><b>
</b></details>

<details>
<summary>What monitoring methods are you familiar with?</summary><br><b>
</b></details>

<a name="devops-advanced"></a>
#### :star: Advanced

<details>
<summary>Tell me how you perform plan capacity for your CI/CD resources (e.g. servers, storage, etc.)</summary><br><b>
</b></details>

<details>
<summary>How would you structure/implement CD for an application which depends on several other applications?</summary><br><b>
</b></details>

<details>
<summary>How do you manage dependencies?</summary><br><b>
</b></details>

<details>
<summary>Explain what are design patterns. Which design patterns are you familiar with?</summary><br><b>
</b></details>

<details>
<summary>How do you measure your CI/CD quality? Are there any metrics you are using?</summary><br><b>
</b></details>

<details>
<summary>What is a configuration drift? What problems is it causing?</summary><br><b>

Configuration drift happens when in an environment of servers with the exact same configuration and software, a certain server
or servers are being applied with updates or configuration which other servers don't get and over time these servers become
slightly different than all others.

This situation might lead to bugs which hard to identify and reproduce.
</b></details>

<details>
<summary>How to deal with configuration drift?</summary><br><b>
</b></details>

<details>
<summary>Do you have experience with testing cross-projects changes? (aka cross-dependency)</summary><br><b>

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.
</b></details>

<details>
<summary>In what scenarios would you prefer to use SQL?</summary><br><b>

  * Homogeneous data, no changes anticipated
  * ACID compliance is important
</b></details>


## Jenkins

<a name="jenkins-beginner"></a>
#### :baby: Beginner

<details>
<summary>What is Jenkins? What have you used it for?</summary><br><b>
</b></details>

<details>
<summary>What are the advantages of Jenkins over its competitors? Can you compare it to one of the following systems?:

  * Travis
  * Bamboo
  * Teamcity
  * CircleCI</summary><br><b>
</b></details>

<details>
<summary>Explain the following:

  * Job
  * Build
  * Plugin
  * Slave
  * Executor</summary><br><b>
</b></details>

<details>
<summary>What plugins have you used in Jenkins?</summary><br><b>
</b></details>

<details>
<summary>Explain CI/CD and how you implemented it in Jenkins</summary><br><b>
</b></details>

<details>
<summary>What type of jobs are there? Which types have you used and why?</summary><br><b>
</b></details>

<details>
<summary>How did you report build results to users? What ways are you familiar with?</summary><br><b>
</b></details>

<details>
<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>
</b></details>

<details>
<summary>How to secure Jenkins?</summary><br><b>
</b></details>

<a name="jenkins-advanced"></a>
#### :star: Advanced

<details>
<summary>How to acquire multiple slaves for one specific build?</summary><br><b>
</b></details>

<details>
<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>
</b></details>

<details>
<summary>Do you have experience with developing a Jenkins plugin? Can you describe this experience?</summary><br><b>
</b></details>

<details>
<summary>If you are managing a dozen of jobs, you can probably use the Jenkins UI. How do you manage the creation and deletion of hundreds of jobs every week/month?</summary><br><b>
</b></details>

<details>
<summary>What are some of Jenkins limitations?<summary><br><b>

  * Testing cross-dependencies (changes from multiple projects together)
  * Starting builds from any stage (although cloudbees implemented something called checkpoints)
</b></details>

<details>
<summary>How would you implement an option of a starting a build from a certain stage and not from the beginning?<summary><br><b>
</b></details>

<details>
<summary>Have you written Jenkins scripts? If yes, what for and how they work?</summary><br><b>
</b></details>

## AWS

<a name="aws-beginner"></a>
#### :baby: Beginner

##### Global Infrastructure

<details>
<summary>Explain the following

  * Availability zone
  * Region
  * Edge location</summary><br><b>
</b>
<b>
AWS regions are data centers hosted across different geographical locations worldwide, each region is completely independant from one another. 
Within each region,There are multiple isolatated locations known as Availability Zones. Multiple availability zones insure high availability in case one of them goes down.

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.
</b>
</details>

##### S3
 
<details>
<summary>Explain what is S3 and what is it used for</summary><br>
<b>
S3 stands for 3 S, Simple Storage Service.
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. while having a maximum size of 5 GB per file (multipart upload if more than 5 GB in size).
</b>
</details>

<details>
<summary>What is a bucket?</summary><br><b>
An S3 bucket is a resource which is similar to folders in a filesystem and allows storing objects, which consist of data and its  metadata.
</b></details>

<details>
<summary>True or False? a bucket name must be globally unique</summary><br><b>
True
</b></details>

<details>
<summary>What objects in S3 consists of?
  * Another way to ask it: explain key, value, version id and metadata in context of objects</summary><br><b>
</b></details>

<details>
<summary>Explain data consistency</summary><br><b>
</b></details>

<details>
<summary>Can you host dynamic websites on s3? what about static websites?</summary><br><b>
</b></details>

<details>
<summary>What security measures have you taken in context of S3?</summary><br><b>
</b></details>

##### CloudFront

<details>
<summary>Explain what is CloudFront and what is it used for</summary><br><b>
</b></details>

<details>
<summary>Explain the following
  * Origin
  * Edge location
  * Distribution</summary><br><b>
</b></details>

<details>
<summary>What delivery methods available for the user with CDN?</summary><br><b>
</b></details>

<details>
<summary>True or False? objects are cached for the life of TTL</summary><br><b>
</b></details>


##### EC2

<details>
<summary>What type of instances have you created?</summary><br><b>
</b></details>

<details>
<summary>How to increase RAM for a given EC2 instance?</summary><br><b>

Stop the instance, the type of the instance to match the desired RAM and start the instance.
</b></details>


## Network

<a name="network-beginner"></a>
#### :baby: Beginner

<details>
<summary>Explain the OSI model. What layers there are? What each layer is responsible for?</summary><br><b>

Application: user end (HTTP is here)
Presentation: establishes context between application-layer entities (Encryption is here)
Session: establishes, manages and terminates the connections
Transport: transfers variable-length data sequences from a source to a destination host (TCP & UDP are here)
Network: transfers datagrams from one network to another (IP is here)
Data link: provides a link between two directly connected nodes (MAC is here)
Physical: the electrical and physical spec the data connection (Bits are here)
</b></details>

<details>
<summary>What delivery schemes are you familiar with?</summary><br><b>

Unitcast: One to one communication where there is one sender and one reciever.

Broadcast: Sending a message to everone in the network. The address ff:ff:ff:ff:ff:ff is used for broadcasting.
           Two common protocols which use broadcast are ARP and DHCP.

Multicast: Sending a message to a group of subscribers. It can be one-to-many or many-to-many.
</b></details>

<details>
<summary>What is CSMA/CD? Is it used in modern ethernet networks?</summary><br><b>

CSMA/CD stands for Carrier Sense Multiple Access / Collision Detection.
Its primarily focus it to manage access to shared medium/bus where only one host can transmit at a given point of time.

CSMA/CD algorithm:

1. Before sending a frame, it checks whether another host already transmitting a frame.
2. If no one transmitting, it starts transmitting the frame.
3. If two hosts transmitted at the same time, we have a collision.
4. Both hosts stop sending the frame and they send to everyone a 'jam signal' notifying everyone that a collision occured
5. They are waiting for a random time before sending again
6. Once each host waited for a raondom time, they try to send the frame again and so the
</b></details>

<details>
<summary>Describe the following network devices and the difference between them: router, switch and hub</summary><br><b>
</b></details>

<details>
<summary>What is NAT?</summary><br><b>
</b></details>

<details>
<summary>What is the difference between TCP and UDP?</summary><br><b>
</b></details>

<details>
<summary>What is ARP? How it works?</summary><br><b>
</b></details>

<details>
<summary>What is DHCP? How it works?</summary><br><b>
</b></details>

<details>
<summary>What is SSL tunneling? How it works?</summary><br><b>
</b></details>

<details>
<summary>What is a socket? Where can you see the list of sockets in your system?</summary><br><b>
</b></details>

<details>
<summary>What is IPv6? Why should we consider using it if we have IPv4?</summary><br><b>
</b></details>

<details>
<summary>What is VLAN?</summary><br><b>
</b></details>

<details>
<summary>What is MTU?</summary><br><b>
</b></details>

<details>
<summary>What is SDN?</summary><br><b>
</b></details>

<details>
<summary>What is ICMP?</summary><br><b>
</b></details>

<details>
<summary>What is NAT? How it works?</summary><br><b>
</b></details>

## Linux

<a name="linux-beginner"></a>
#### :baby: Beginner

<details>
<summary>Explain what each of the following commands does and given an example on how to use it:

  * ls
  * rm 
  * rmdir (can you achieve the same result by using <code>rm</code>?)
  * grep
  * wc
  * touch
  * df</summary><br><b>
</b></details>

<details>
<summary>How to make sure a service will start on a OS of your choice?</summary><br><b>
</b></details>

<details>
<summary>How do you schedule tasks periodically?</summary><br><b>

You can use the commands <code>cron</code> and <code>at</code>.
With cron, tasks are scheduled using the following format:

<minute> <hour> <day of month> <month> <day of week> <command to execute>

The tasks are stored in a cron file.
</b></details>

##### Permissions

<details>
<summary>How to change the permissions of a file?</summary><br><b>
</b></details>

<details>
<summary>What does the following permissions mean?:

  * 777
  * 644
  * 750</summary><br><b>
</b></details>

<details>
<summary>Explain what is setgid, setuid and sticky bit</summary><br><b>
</b></details>

<details>
<summary>How to add a new user to the system without providing him the ability to log-in into the system?</summary><br><b>
</b></details>

<details>
<summary>What commands are you using for troubleshooting issues? specifically:

  * Disk issues
  * Memory, CPU issues
  * Networking issues</summary><br><b>
</b></details>

<details>
<summary>What is the difference between Linux and Unix?</summary><br><b>
</b></details>

<details>
<summary>Are you familiar with the following process monitoring tools and commands?:

  * top
  * ps
  * htop
  * atop
  * lsof
Can you explain when are you using each one?</summary><br><b>
</b></details>

<details>
<summary>What is a Linux kernel module and how do you load a new module?</summary><br><b>
</b></details>

<details>
<summary>What is KVM?</summary><br><b>
</b></details>

<details>
<summary>Explain redirection</summary><br><b>
</b></details>

<details>
<summary>What are wildcards? Can you give an example of how to use them?</summary><br><b>
</b></details>

<details>
<summary>What do we grep for in each of the following commands?:

  * <code>grep '[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}' some_file</code>
  * <code>grep -E "error|failure" some_file</code>
  * <code>grep '[0-9]$' some_file</code>
</summary><br><b>

1. An IP address
2. The word "error" or "failure"
3. Lines which end with a number
</b></details>

<details>
<summary>Tell me everything you know about Linux boot process</summary><br><b>
</b></details>

<details>
<summary>What is an exit code? What exit codes are you familiar with?</summary><br><b>

An exit code (or return code) represents the code returned by a child process to its
parent process.

0 is an exit code which represents success while anything higher than 1 represents error.
Each number has different meaning, based on how the application was developed.

I consider this as a good blog post to read more about it: https://shapeshed.com/unix-exit-codes
</b></details>

<details>
<summary>What is the different between a soft link and hard link?</summary><br><b>

hard link is the same file, using the same inode.
soft link is a shortcut to another file, using a different inode.

soft links can be created between different file systems while
hard link can be created only within the same file system.
</b></details>

<details>
<summary>What is a swap partition? What is it used for?</summary><br><b>
</b></details>

<details>
<summary>What do you know about LVM?</summary><br><b>
</b></details>

<details>
<summary>Explain the following in regards to LVM:

  * PV
  * VG
  * LV</summary><br><b>
</b></details>

<details>
<summary>What RAID is used for? Can you explain the differences between RAID 0, 1, 5 and 10?</summary><br><b>
</b></details>

<details>
<summary>What is lazy umount?</summary><br><b>
</b></details>

<details>
<summary>Fix the following commands:

  * sed "s/1/2/g' /tmp/myFile
  * find . -iname \*.yaml -exec sed -i "s/1/2/g" {} ;</summary><br><b>
</b></details>

<details>
<summary>Explain what is stored in each of the following paths and if there is anything unique about it:</summary><br><b>

  * /tmp
  * /var/log
  * /bin
  * /proc
  * /usr/local
</b></details>

<details>
<summary>How to run a process in the background and why to do that in the first place?</summary><br><b>

You can achieve that by specifying & at end of the command.
As to why, since some commands/processes can take a lot of time to finish
execution or run forever
</b></details>

<details>
<summary>What signal is used when you run 'kill <process id>'?</summary><br><b>

The default signal is SIGTERM (15). This signal kills
process gracefully which means it allows it to save current
state configuration.
</b></details>

<details>
<summary>What signals are you familiar with?</summary><br><b>

SIGTERM - default signal for terminating a process
SIGHUP - common usage is for reloading configuration
SIGKILL - a signal which cannot caught or ignored

To view all available signals run `kill -l`
</b></details>

<details>
<summary>What are daemons?</summary><br><b>
</b></details>

<details>
<summary>What are the possible states of a process in Linux?</summary><br><b>

Running
Waiting
Stopped
Terminated
Zombie
</b></details>

<details>
<summary>What is the init process?</summary><br><b>
</b></details>

<details>
<summary>How to change the priority of a process? Why would you want to do that?</summary><br><b>
</b></details>

<details>
<summary>What are system calls? What system calls are you familiar with?</summary><br><b>
</b></details>

<details>
<summary>Find all the files which end with '.yml' and replace the number 1 in 2 in each file</summary><br><b>

ind /some_dir -iname \*.yml -print0 | xargs -0 -r sed -i "s/1/2/g"
</b></details>

<details>
<summary>How to check how much free memory a system has? How to check memory consumption by each process?</summary><br><b>

You can use the commands <code>top</code> and <code>free</code>
</b></details>

<details>
<summary>How would you split a 50 lines file into 2 files of 25 lines each?</summary><br><b>

You can use the <code>split</code> command this way: <code>split -l 25 some_file</code>
</b></details>

<details>
<summary>What is a file descriptor? What file descriptors are you familiar with?</summary><br><b>

File descriptor, also known as file handler, is a unique number which identifies an open file in the operating system.

In Linux (and Unix) the first three file descriptors are:
  * 0 - the default data stream for input
  * 1 - the default data stream for output
  * 2 - the default data stream for output related to errors

This is a great article on the topic: https://www.computerhope.com/jargon/f/file-descriptor.htm
</b></details>

<details>
<summary>What's an inode?</summary><br><b>

For each file (and directory) in Linux there is an inode, a data structure which stores metadata
related to the file like its size, owner, permissions, etc.
</b></details>

<details>
<summary>How to list active connections?</summary><br><b>
</b></details>

<details>
<summary>What is NTP? What is it used for?</summary><br><b>
</b></details>

<details>
<summary>What is SELiunx?</summary><br><b>
</b></details>

<details>
<summary>What is nftables?</summary><br><b>
</b></details>

<details>
<summary>What firewalld daemon is responsible for?</summary><br><b>
</b></details>

##### DNS

<details>
<summary>What the file <code>/etc/resolv.conf</code> is used for? What does it include?</summary><br><b>
</b></details>

<details>
<summary>What is a "A record"?</summary><br><b>
</b></details>

<details>
<summary>What is a PTR record?</summary><br><b>

While an A record points a domain name to an IP address, a PTR record does the opposite and resolves the IP address to a domain name.
</b></details>

<details>
<summary>What is a MX record?</summary><br><b>
</b></details>

<details>
<summary>Is DNS using TCP or UDP?</summary><br><b>
</b></details>

##### Packaging

<details>
<summary>Do you have experience with packaging? Can you explain how it works?</summary><br><b>
</b></details>

<details>
<summary>RPM: explain the spec format(what it should and can include)</summary><br><b>
</b></details>

<a name="linux-advanced"></a>
#### :star: Advanced

<details>
<summary>What happens in the OS when you execute <code>ls</code>?</summary><br><b>
</b></details>

<details>
<summary>How processes are being created?</summary><br><b>
</b></details>

<details>
<summary>When you run <code>ip a</code> you see there is a device called 'lo'. What is it and why do we need it?</summary><br><b>
</b></details>

<details>
<summary>What <code>traceroute</code> command does? How it works?</summary><br><b>
</b></details>

<details>
<summary>What is the routing table? How do you view it?</summary><br><b>
</b></details>

<details>
<summary>What are cgroups? In what scenario would you use them?</summary><br><b>
</b></details>

<details>
<summary>How to create a file of a certain size?</summary><br><b>

There are a couple of ways to do that:
  
  * dd if=/dev/urandom of=new_file.txt bs=2MB count=1
  * truncate -s 2M new_file.txt
  * fallocate -l 2097152 new_file.txt
</b></details>

<details>
<summary>What are the differences between the following system calls?: exec(), fork(), vfork() and clone()?</summary><br><b>
</b></details>

<details>
<summary>Explain Process Descriptor and Task Structure</summary><br><b>
</b></details>

<details>
<summary>What are the differences between threads and processes?</summary><br><b>
</b></details>

<details>
<summary>Explain Kernel Threads</summary><br><b>
</b></details>

<details>
<summary>What happens when socket system call is used?</summary><br><b>

This is a good article about the topic: https://ops.tips/blog/how-linux-creates-sockets
</b></details>


## Ansible

<details>
<summary>Describe each of the following components in Ansible, including the relationship between them:

  * Task
  * Module
  * Play
  * Playbook
  * Role</summary><br><b>

Task – a call to a specific Ansible module
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 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.
</b></details>

<details>
<summary>What is an inventory file and how you define one?</summary><br><b>

An inventory file defines hosts and/or groups of hosts on which Ansible tasks executed upon.

An example of inventory file:

192.168.1.2
192.168.1.3
192.168.1.4

[web_servers]
190.40.2.20
190.40.2.21
190.40.2.22
</b></details>

<details>
<summary>What is a dynamic inventory file? When you would use one?</summary><br><br>

A dynamic inventory file tracks hosts from one or more sources like cloud providers and CMDB systems.

You should use one when using external sources and especially when the hosts in your environment are being automatically<br>
spun up and shut down, without you tracking every change in these sources.
</b></details>

<details>
<summary>You want to run Ansible playbook only on specific minor version of your OS, how would you achieve that?</summary><br><b>
</b></details>

<details>
<summary>Write a task to create the directory ‘/tmp/new_directory’</summary><br><b>

```
- name: Create a new directory
  file:
      path: "/tmp/new_directory"
      state: directory
```
</b></details>

<details>
<summary>What would be the result of the following play?</summary><br><b>

```
---
- name: Print information about my host
  hosts: localhost
  gather_facts: 'no'                                                                                                                                                                           
  tasks:
      - name: Print hostname
        debug:
            msg: "It's me, {{ ansible_hostname }}"
```

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.
</b></details>

<details>
<summary>Write a playbook to install ‘zlib’ and ‘vim’ on all hosts if the file ‘/tmp/mario’ exists on the system.</summary><br><b>

```
---
- hosts: all
  vars:
      mario_file: /tmp/mario
      package_list:
          - 'zlib' 
          - 'vim'
  tasks:
      - name: Check for mario file
        stat:
            path: "{{ mario_file }}"
        register: mario_f

      - name: Install zlib and vim if mario file exists
        become: "yes"
        package:
            name: "{{ item }}"
            state: present
        with_items: "{{ package_list }}"
        when: mario_f.stat.exists
```
</b></details>

<details>
<summary>Write a playbook to deploy the file ‘/tmp/system_info’ on all hosts except for controllers group, with the following content</summary><br><b>

  ```
  I'm <HOSTNAME> and my operating system is <OS>
  ```

  replace <HOSTNAME> and  <OS> with the actual data for the specific host you are running on

The playbook to deploy the system_info file

```
--- 
- name: Deploy /tmp/system_info file
  hosts: all:!controllers
  tasks: 
      - name: Deploy /tmp/system_info
        template:
            src: system_info.j2 
            dest: /tmp/system_info
```

The content of the system_info.j2 template

```
# {{ ansible_managed }}
I'm {{ ansible_hostname }} and my operating system is {{ ansible_distribution }
```
</b></details>

<details>
<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 the link above. Also, note there is a significant difference between Ansible 1.x and 2.x.
</b></details>

## Terraform


#### :baby: Beginner

<details>
<summary>Can you explain what is Terraform? How it works?</summary><br><b>

Read [here](https://www.terraform.io/intro/index.html#what-is-terraform-)
</b></details>

<details>
<summary>What benefits infrastructure-as-code has?</summary><br><b>

- fully automated process of provisioning, modifying and deleting your infrastructure
- version control for your infrastructure which allows you to quickly rollback to previous versions
- validate infrastructure quality and stability with automated tests and code reviews
- makes infrastructure tasks less repetitive
</b></details>

<details>
<summary>Why Terraform and not other technologies? (e.g. Ansible, Puppet, CloufFormation)</summary><br><b>

A common *wrong* answer is to say that Ansible and Puppet are configuration management tools
and Terraform is a provisioning tool. While technically true, it doesn't mean Ansible and Puppet can't
be used for provisioning infrastructure. Also, it doesn't explains why Terraform should be used over
CloudFormation if at all.

The benefits of Terraform over the other tools:
  * it follows the immutable infrastructure approach which has benefits like avoiding a configuration drift over time
  * Ansible and Puppet are more procedural (you mention what to execute in each step) and Terraform is declartive 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 terrform you specify 2, in Ansible and puppet you have to only provision 1 additional server
</b></details>

<details>
<summary>Explain what the following commands do:

  * <code>terraform init</code>
  * <code>terraform plan</code>
  * <code>terraform apply</code>
</summary><br><b>

<code>terraform init</code> scans your code to figure which providers are you using and download them.
<code>terraform plan</code> will let you see what terraform is about to do before actually doing it.
<code>terraform apply</code> will provision the resources specified in the .tf files.
</b></details>

<details>
<summary>How to write down a variable which changes by an external source or during <code>terraform apply</code>?</summary><br><b>

You use it this way: <code>variable “my_var” {}</code>
</b></details>


## Docker

<a name="docker-beginner"></a>

#### :baby: beginner

<details>
<summary>How containers are different from VMs?</summary><br><b>

The primary difference between containers and VMs is that containers allow you to virtualize
multiple workloads on the operating system while in the case of VMs the hardware is being virtualized to
run multiple machines each with its own OS.
</b></details>

<details>
<summary>In which scenarios would you use containers and in which you would prefer to use VMs?</summary><br><b>

You should choose VMs when:
  * you need run an application which requires all the resources and functionalilies of an OS
  * you need full isolation and security

You should choose containers when:
  * you need a lightweight solution that quickly starts
  * Running multiple versions or instances of a single application
</b></details>

<details>
<summary>What happens when you run `docker run hello-world`?</summary><br><b>

Docker CLI passes your request to Docker daemon.
Docker daemon downloads the image from Docker Hub
Docker daemon creates a new container by using the image it downloaded
Docker daemon redirects output from container to Docker CLI which redirects it to the standard output
</b></details>

<details>
<summary>How do you run a container?</summary><br><b>
</b></details>

<details>
<summary>What do you see when you run `docker ps`?</summary><br><b>
</b></details>

<details>
<summary>What `docker commit` does? when will you use it?</summary><br><b>
</b></details>

<details>
<summary>How would you transfer data from one container into another?</summary><br><b>
</b></details>

<details>
<summary>What is the difference between ADD and COPY in Dockerfile?</summary><br><b>
</b></details>

<details>
<summary>What is the difference between CMD and RUN in Dockerfile?</summary><br><b>
</b></details>

<details>
<summary>Explain what is Docker compose and what is it used for</summary><br><b>
</b></details>

<details>
<summary>What are the differences between Docker compose, Docker swarm and Kuberenets?</summary><br><b>
</b></details>

<details>
<summary>Explain Docker interlock</summary><br><b>
</b></details>

<details>
<summary>What is the difference between Docker Hub and Docker cloud?</summary><br><b>

Docker Hub is a native Docker registry service which allows you to run pull
and push commands to install and deploy Docker images from the Docker Hub.

Docker Cloud is built on top of the Docker Hub so Docker Cloud provides
you with more options/features compared to Docker Hub. One example is
Swarm management which means you can create new swarms in Docker Cloud.
</b></details>

<details>
<summary>Explain image layers</summary><br><b>
</b></details>

## Kubernetes

<a name="kubernetes-beginner"></a>
#### :baby: Beginner

<details>
<summary>What is Kubernetes?</summary><br><b>
</b></details>

<details>
<summary>Why Docker isn't enough? Why do we need Kubernetes?</summary><br><b>
</b></details>

<details>
<summary>Describe the architecture of Kuberenets</summary><br><b>
</b></details>

<details>
<summary>How do you monitor your Kuberenets?</summary><br><b>
</b></details>

<details>
<summary>What is kubectl? How do you use it?</summary><br><b>
</b></details>

<details>
<summary>What is kubconfig? What do you use it for?</summary><br><b>
</b></details>

<details>
<summary>How do you create users? Where user information is stored?</summary><br><b>
</b></details>


## Python

<a name="python-beginner"></a>
#### :baby: Beginner

<details>
<summary>What data type supported in Python and which of them are mutable?
  What function can you use to show that a certain data type is mutable?</summary><br><b>

The mutable data types are:

    List
    Dictionary
    Set
    
The immutable data types are:

    Numbers (int, float, ...)
    String
    Bool
    Tuple

The id function can be used to check if a given variable is mutable or not.
</b></details>

<details>
<summary>What is PEP8? Give an example of 5 style guidelines</summary><br><b>

PEP8 is a list of coding conventions and style guidelines for Python

5 style guidelines:

    1. Limit all lines to a maximum of 79 characters.
    2. Surround top-level function and class definitions with two blank lines.
    3. Use commas when making a tuple of one element
    4. Use spaces (and not tabs) for indentation
    5. Use 4 spaces per indentation level
</b></details>

<details>
<summary>Write a program which will revert a string (e.g. pizza -> azzip)</summary><br><b>

```
Shortest way is str[::-1]

"Classic" way:
```
</b></details>

<details>
<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
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").
</b></details>

<details>
<summary>Sort a list of lists by the second item of each nested list</summary><br><b>

```
li = [[1, 4], [2, 1], [3, 9], [4, 2], [4, 5]]

sorted(x, key=lambda l: l[1])
```
</b></details>

<details>
<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>

```
set([food for bro in x for food in bro['food']])
```
</b></details>

<details>
<summary>What is List Comprehension? Is better than a typical loop? Why?</summary><br><b>
</b></details>

<details>
<summary>How to reverse a string?</summary><br><b>

Shortest way is: <code>my_string[::-1]</code> but it doesn't mean it's the most efficient one.
</b></details>

<details>
<summary>Write a function to determine if a given string is a palindrome</summary><br><b>
</b></details>

<details>
<summary>Explain what is GIL</summary><br><b>
</b></details>

<a name="python-advanced"></a>
#### :star: Advanced

<details>
<summary>Explain what is a decorator</summary><br><b>
</b></details>

<details>
<summary>Can you show how to write and use decorators?</summary><br><b>
</b></details>

<details>
<summary>Are you familiar with Dataclasses? Can you explain what are they used for?</summary><br><b>
</b></details>

<details>
<summary>Explain Context Manager</summary><br><b>
</b></details>

<details>
<summary>Explain the Buffer Protocol</summary><br><b>
</b></details>

<details>
<summary>Explain Descriptors</summary><br><b>
</b></details>

## Prometheus

<details>
<summary>Describe the following Prometheus components:
  - Prometheus server
  - Push Gateway
  - Alert Manager</summary><br><b>

Prometheus server responsible for scraping the storing the data<br>
Push gateway is used for short-lived jobs<br>
Alert manager is responsible for alerts ;)
</b></details>

<details>
<summary>What is an exporter? What is it used for?</summary><br><b>
</b></details>

## Git

<a name="git-beginner"></a>
#### :baby: Beginner

<details>
<summary>What is the difference between <code>git pull</code> and <code>git fetch</code>?</summary><br><b>

Shortly, git pull = git fetch + git merge

When you run git pull, it gets all the changes from the remote or central
repository and attaches it to your corresponding branch in your local reposistory.

git fetch gets all the changes from the remote repository, stores the changes in
a separate branch in your local repository
</b></details>

<details>
<summary>Explain the following: <code>git directory</code>, <code>working directory</code> and <code>staging area</code></summary><br><b>

The Git directory is where Git stores the metadata 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)
</b></details>

<details>
<summary>How to resolve git merge conflicts?</summary><br><b>

<p>
First, you open the files which are in conflict and identify what are the conflicts.
Next, based on what is accepted in your company or team, you either discuss with your
colleagues on the conflicts or resolve them by yourself
After resolving the conflicts, you add the files with `git add <file_name>`
Finally, you run `git rebase --continue`
</p>
</b></details>

<details>
<summary>What is the difference between <code>git reset</code> and <code>git revert</code>?</summary><br><b>

<p>

`git revert` creates a new commit which undoes the changes from last commit.

`git reset` depends on the usage, can modify the index or change the commit which the branch head
is currently pointing at.
</p>
</b></details>

<details>
<summary>You would like to move forth commit to the top. How would you achieve that?</summary><br><b>

Using <code>git rebase></code> command
</b></details>

<details>
<summary>In what situations are you using <code>git rebase</code>?</summary><br><b>
</b></details>

<details>
<summary>What merge strategies are you familiar with?</summary><br><b>

Mentioning two or three should be enough and it's probably good to mention that 'recursive' is the default one.

recursive
resolve
ours
theirs

This page explains it the best: https://git-scm.com/docs/merge-strategies
</b></details>

<a name="git-advanced"></a>
#### :star: Advanced

<details>
<summary>Explain Git octopus merge</summary><br><b>

Probably good to mention that it's:

  * It's good for cases of merging more than one branch (and also the default of such use cases)
  * It's primarily meant for bundling topic branches together 

This is a great article about Octopus merge: http://www.freblogg.com/2016/12/git-octopus-merge.html
</b></details>

## Go

<a name="go-beginner"></a>
#### :baby: Beginner

<details>
<summary>What are some characteristics of the Go programming language?</summary><br><b>

  * Strong and static typing - the type of the variables can't be changed over time and they have to be defined at compile time
  * Simplicity 
  * Fast compile times
  * Built-in concurrency
  * Garbage collected
  * Platform independent
  * Compile to standalone binary - anything you need to run your app will be compiled into one binary. Very useful for version management in run-time. 

Go also has good community.
</b></details>

<details>
<summary>What is the difference between <code>var x int = 2</code> and <code>x := 2</code>?</summary><br><b>

The result is the same, a variable with the variable 2.

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.
</b></details>

<details>
<summary>What libraries of Go have you used?</summary><br><b>

This should be answered based on your usage but some examples are:

  * fmt - formatted I/O
</b></details>

<details>
<summary>Write an "hello world" program?</summary><br><b>

```
package main

import "fmt"

func main() {
        fmt.Println("Hello World")
}
```
</b></details>

## Mongo

<a name="mongo-beginner"></a>
#### :baby: Beginner

<details>
<summary>In what scenarios would you prefer to use NoSQL/Mongo over SQL?</summary><br><b>

  * Heterogeneous data which changes often
  * Data consistency and integrity is not top priority
</b></details>

<details>
<summary>What is a document? What is a collection?</summary><br><b>
</b></details>

<details>
<summary>What is an aggregator?</summary><br><b>
</b></details>

## OpenShift

<a name="openshift-beginner"></a>
#### :baby: Beginner

<details>
<summary>What is OpenShift? Did you use it? If yes, how?</summary><br><b>
</b></details>

<details>
<summary>Can you explain the difference between OpenShift and Kubernetes?</summary><br><b>
</b></details>

<details>
<summary>Define Pods and explain what are stateful pods</summary><br><b>
</b></details>

<details>
<summary>What types of build strategies are you familiar with?</summary><br><b>
</b></details>

<details>
<summary>Explain what are labels and what they are used for</summary><br><b>
</b></details>

<details>
<summary>Explain what are annotations and how they are different from labels</summary><br><b>
</b></details>

<details>
<summary>Explain what is Downward API</summary><br><b>
</b></details>

## Shell Scripting

<a name="shell-scripting-beginner"></a>
#### :baby: Beginner

<details>
<summary>Tell me about your experience with shell scripting</summary><br><b>
</b></details>

<details>
<summary>What this line in scripts mean?: <code>#!/bin/bash</code></summary><br><b>
</b></details>

<details>
<summary>What do you tend to include in every script you write?</summary><br><b>
</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 but in Bash for example, by default the script will keep running.
</b></details>

<details>
<summary>Today we have tools and technologies like Ansible. Why would someone still use shell scripting?</summary><br><b>
</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>
</b></details>

<details>
<summary>How do you get input from the user in shell scripts?</summary><br><b>
</b></details>

<details>
<summary>Explain conditionals and how do you use them</summary><br><b>
</b></details>

<details>
<summary>What is a loop? What types of loops are you familiar with?</summary><br><b>
</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>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>


<a name="shell-scripting-advanced"></a>
#### Advanced

<details>
<summary>Explain the following code:

<code>:(){ :|:& };:</code>

</summary><br><b>
</b></details>

## Scenarios

Scenarios are questions which don't have verbal answer and require you one of the following:

  * Set up environments
  * Write scripts
  * Design and/or develop infrastructure projects

These questions usually given as an home task to the candidate and they can combine several topics together.
Below you can find several scenario questions:

* [Elasticsearch & Kibana on AWS](scenarios/elk_kibana_aws.md)
* [Ansible, Minikube and Docker](scenarios/ansible_minikube_docker.md)
* [Cloud Slack bot](scenarios/cloud_slack_bot.md)
* [Writing Jenkins Scripts](scenarios/jenkins_scripts.md)
* [Writing Jenkins Pipelines](scenarios/jenkins_pipelines.md)