opentelemetry-go/website_docs/manual.md

---
title: Manual Instrumentation
weight: 3
linkTitle: Manual
aliases: [/docs/instrumentation/go/instrumentation, /docs/instrumentation/go/manual_instrumentation]
---

Instrumentation is the process of adding observability code to your application. There are two general types of instrumentation - automatic, and manual - and you should be familiar with both in order to effectively instrument your software.

## Getting a Tracer

To create spans, you'll need to acquire or initialize a tracer first.

### Initiallizing a new tracer

Ensure you have the right packages installed:

```
go get go.opentelemetry.io/otel \
  go.opentelemetry.io/otel/trace \
  go.opentelemetry.io/otel/sdk \
```

Then initialize an exporter, resources, tracer provider, and finally a tracer.

```go
package app

import (
	"context"
	"fmt"
	"log"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
	"go.opentelemetry.io/otel/sdk/resource"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.7.0"
	"go.opentelemetry.io/otel/trace"
)

var tracer trace.Tracer

func newExporter(ctx context.Context)  /* (someExporter.Exporter, error) */ {
	// Your preferred exporter: console, jaeger, zipkin, OTLP, etc.
}

func newTraceProvider(exp sdktrace.SpanExporter) *sdktrace.TracerProvider {
    // The service.name attribute is required.
	resource := resource.NewWithAttributes(
		semconv.SchemaURL,
		semconv.ServiceNameKey.String("ExampleService"),
	)

	return sdktrace.NewTracerProvider(
		sdktrace.WithBatcher(exp),
		sdktrace.WithResource(resource),
	)
}

func main() {
	ctx := context.Background()

	exp, err := newExporter(ctx)
	if err != nil {
		log.Fatalf("failed to initialize exporter: %v", err)
	}

	// Create a new tracer provider with a batch span processor and the given exporter.
	tp := newTraceProvider(exp)

	// Handle shutdown properly so nothing leaks.
	defer func() { _ = tp.Shutdown(ctx) }()

	otel.SetTracerProvider(tp)

	// Finally, set the tracer that can be used for this package.
	tracer = tp.Tracer("ExampleService")
}
```

You can now access `tracer` to manually instrument your code.

## Creating Spans

Spans are created by tracers. If you don't have one initialized, you'll need to do that.

To create a span with a tracer, you'll also need a handle on a `context.Context` instance. These will typically come from things like a request object and may already contain a parent span from an [instrumentation library][].

```go
func httpHandler(w http.ResponseWriter, r *http.Request) {
	ctx, span := tracer.Start(r.Context(), "hello-span")
	defer span.End()

	// do some work to track with hello-span
}
```

In Go, the `context` package is used to store the active span. When you start a span, you'll get a handle on not only the span that's created, but the modified context that contains it.

Once a span has completed, it is immutable and can no longer be modified.

### Get the current span

To get the current span, you'll need to pull it out of a `context.Context` you have a handle on:

```go
// This context needs contain the active span you plan to extract.
ctx := context.TODO()
span := trace.SpanFromContext(ctx)

// Do something with the current span, optionally calling `span.End()` if you want it to end
```

This can helpful if you'd like to add information to the current span at a point in time.

### Create nested spans

You can create a nested span to track work in a nested operation.

If the current `context.Context` you have a handle on already contains a span inside of it, creating a new span makes it a nested span. For example:

```go
func parentFunction(ctx context.Context) {
	ctx, parentSpan := tracer.Start(ctx, "parent")
	defer parentSpan.End()

	// call the child function and start a nested span in there
	childFunction(ctx)

	// do more work - when this function ends, parentSpan will complete.
}

func childFunction(ctx context.Context) {
	// Create a span to track `childFunction()` - this is a nested span whose parent is `parentSpan`
	ctx, childSpan := tracer.Start(ctx, "child")
	defer childSpan.End()

	// do work here, when this function returns, childSpan will complete.
}
```

Once a span has completed, it is immutable and can no longer be modified.

### Span Attributes

Attributes are keys and values that are applied as metadata to your spans and are useful for aggregating, filtering, and grouping traces. Attributes can be added at span creation, or at any other time during the lifecycle of a span before it has completed.

```go
// setting attributes at creation...
ctx, span = tracer.Start(ctx, "attributesAtCreation", trace.WithAttributes(attribute.String("hello", "world")))
// ... and after creation
span.SetAttributes(attribute.Bool("isTrue", true), attribute.String("stringAttr", "hi!"))
```

Attribute keys can be precomputed, as well:

```go
var myKey = attribute.Key("myCoolAttribute")
span.SetAttributes(myKey.String("a value"))
```

#### Semantic Attributes

Semantic Attributes are attributes that are defined by the [OpenTelemetry Specification][] in order to provide a shared set of attribute keys across multiple languages, frameworks, and runtimes for common concepts like HTTP methods, status codes, user agents, and more. These attributes are available in the `go.opentelemetry.io/otel/semconv/v1.7.0` package.

For details, see [Trace semantic conventions][].

### Events

An event is a human-readable message on a span that represents "something happening" during it's lifetime. For example, imagine a function that requires exclusive access to a resource that is under a mutex. An event could be created at two points - once, when we try to gain access to the resource, and another when we acquire the mutex.

```go
span.AddEvent("Acquiring lock")
mutex.Lock()
span.AddEvent("Got lock, doing work...")
// do stuff
span.AddEvent("Unlocking")
mutex.Unlock()
```

A useful characteristic of events is that their timestamps are displayed as offsets from the beginning of the span, allowing you to easily see how much time elapsed between them.

Events can also have attributes of their own -

```go
span.AddEvent("Cancelled wait due to external signal", trace.WithAttributes(attribute.Int("pid", 4328), attribute.String("signal", "SIGHUP")))
```

## Creating Metrics

The metrics API is currently unstable, documentation TBA.

## Propagators and Context

Traces can extend beyond a single process. This requires _context propagation_, a mechanism where identifiers for a trace are sent to remote processes.

In order to propagate trace context over the wire, a propagator must be registered with the OpenTelemetry API.

```go
import (
  "go.opentelemetry.io/otel"
  "go.opentelemetry.io/otel/propagation"
)
...
otel.SetTextMapPropagator(propagation.TraceContext{})
```

> OpenTelemetry also supports the B3 header format, for compatibility with existing tracing systems (`go.opentelemetry.io/contrib/propagators/b3`) that do not support the W3C TraceContext standard.

After configuring context propagation, you'll most likely want to use automatic instrumentation to handle the behind-the-scenes work of actually managing serializing the context.

[OpenTelemetry Specification]: {{< relref "/docs/reference/specification" >}}
[Trace semantic conventions]: {{< relref "/docs/reference/specification/trace/semantic_conventions" >}}
[instrumentation library]: {{< relref "libraries" >}}