Manual Instrumentation

Manual instrumentation is the process of adding observability code to your application.

A note on terminology

.NET is different from other languages/runtimes that support OpenTelemetry. Tracing is implemented by the System.Diagnostics API, repurposing existing constructs like ActivitySource and Activity to be OpenTelemetry-compliant under the covers.

However, there are parts of the OpenTelemetry API and terminology that .NET developers must still know to be able to instrument their applications, wich are covered here as well as the System.Diagnostics API.

If you prefer to use OpenTelemetry APIs instead of System.Diagnostics APIs, you can refer to the OpenTelemetry API Shim docs for tracing.

Initializing tracing

There are two main ways to initialize tracing, depending on whether you’re using a console app or something that’s ASP.NET Core-based.

Console app

To start tracing in a console app, you need to create a tracer provider.

First, ensure that you have the right packages:

dotnet add package OpenTelemetry
dotnet add package OpenTelemetry.Exporter.Console

And then use code like this at the beginning of your program, during any important startup operations.

using OpenTelemetry;
using OpenTelemetry.Trace;
using OpenTelemetry.Resources;

// ...

var serviceName = "MyServiceName";
var serviceVersion "1.0.0";

using var tracerProvider = Sdk.CreateTracerProviderBuilder()
    .AddSource(serviceName)
    .SetResourceBuilder(
        ResourceBuilder.CreateDefault()
            .AddService(serviceName: serviceName, serviceVersion: serviceVersion))
    .AddConsoleExporter()
    .Build();

//...

This is also where you can configure instrumentation libraries.

Note that this sample uses the Console Exporter. If you are exporting to another endpoint, you’ll have to use a different exporter.

ASP.NET Core

To start tracing in an ASP.NET Core-based app, use the OpenTelemetry extensions for ASP.NET Core setup.

First, ensure that you have the right packages:

dotnet add package OpenTelemetry --prerelease
dotnet add package OpenTelemetry.Extensions.Hosting --prerelease
dotnet add package OpenTelemetry.Exporter.Console --prerelease

And then configure it in your ASP.NET Core startup routine where you have access to an IServiceCollection.

using OpenTelemetry;
using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

// Define some important constants and the activity source.
// These can come from a config file, constants file, etc.
var serviceName = "MyCompany.MyProduct.MyService";
var serviceVersion = "1.0.0";

var builder = WebApplication.CreateBuilder(args);

// Configure important OpenTelemetry settings, the console exporter, and automatic instrumentation
builder.Services.AddOpenTelemetryTracing(b =>
{
    b
    .AddConsoleExporter()
    .AddSource(serviceName)
    .SetResourceBuilder(
        ResourceBuilder.CreateDefault()
            .AddService(serviceName: serviceName, serviceVersion: serviceVersion))
});

This is also where you can configure instrumentation libraries.

Note that this sample uses the Console Exporter. If you are exporting to another endpoint, you’ll have to use a different exporter.

Setting up an ActivitySource

Once tracing is initialized, you can configure an ActivitySource, which will be how you trace operations with Activitys.

Typically, an ActivitySource is instantiated once per app/service that is being instrumented, so it’s a good idea to instantiate it once in a shared location. It is also typically named the same as the Service Name.

using System.Diagnostics;

public static class Telemetry
{
    //...

    // Name it after the service name for your app.
    // It can come from a config file, constants file, etc.
    public static readonly ActivitySource MyActivitySource = new(TelemetryConstants.ServiceName);

    //...
}

You can instantiate several ActivitySources if that suits your scenario, although it is generally sufficient to just have one defined per service.

Creating Activities

To create an Activity, give it a name and create it from your ActivitySource.

using var myActivity = MyActivitySource.StartActivity("SayHello");

// do work that 'myActivity' will now track

Creating nested Activities

If you have a distinct sub-operation you’d like to track as a part of another one, you can create activities to represent the relationship.

public static void ParentOperation()
{
    using var parentActivity = MyActivitySource.StartActivity("ParentActivity");

    // Do some work tracked by parentActivity

    ChildOperation();

    // Finish up work tracked by parentActivity again
}

public static void ChildOperation()
{
    using var childActivity = MyActivitySource.StartActivity("ChildActivity");

    // Track work in ChildOperation with childActivity
}

When you view spans in a trace visualization tool, ChildActivity will be tracked as a nested operation under ParentActivity.

Nested Activities in the same scope

You may wish to create a parent-child relationsip in the same scope. Although possible, this is generally not recommended because you need to be careful to end any nested Activity when you expect it to end.

public static void DoWork()
{
    using var parentActivity = MyActivitySource.StartActivity("ParentActivity");

    // Do some work tracked by parentActivity

    using (var childActivity = MyActivitySource.StartActivity("ChildActivity"))
    {
        // Do some "child" work in the same function
    }

    // Finish up work tracked by parentActivity again
}

In the preceding example, childOperation is ended because the scope of the using block is explicitly defined, rather than scoped to DoWork itself like parentOperation.

Get the current Activity

Sometimes it’s helpful to access whatever the current Activity is at a point in time so you can enrich it with more information.

var activity = Activity.Current;
// may be null if there is none

Note that using is not used in the prior example. Doing so will end current Activity, which is not likely to be desired.

Add tags to an Activity

Tags (the equivalent of Attributes in OpenTelemetry) let you attach key/value pairs to an Activity so it carries more information about the current operation that it’s tracking.

using var myActivity = MyActivitySource.StartActivity("SayHello");

activity?.SetTag("operation.value", 1);
activity?.SetTag("operation.name", "Saying hello!");
activity?.SetTag("operation.other-stuff", new int[] { 1, 2, 3 });

Adding events

An event is a human-readable message on an Activity that represents “something happening” during its lifetime. You can think of it like a primitive log.

using var myActivity = MyActivitySource.StartActivity("SayHello");

// ...

myActivity?.AddEvent(new("Gonna try it!"));

// ...

myActivity?.AddEvent(new("Did it!"));

Events can also be created with a timestamp and a collection of Tags.

using var myActivity = MyActivitySource.StartActivity("SayHello");

// ...

myActivity?.AddEvent(new("Gonna try it!", DateTimeOffset.Now));

// ...

var eventTags = new Dictionary<string, object?>
{
    { "foo", 1 },
    { "bar", "Hello, World!" },
    { "baz", new int[] { 1, 2, 3 } }
};

myActivity?.AddEvent(new("Gonna try it!", DateTimeOffset.Now, new(eventTags)));

An Activity can be created with zero or more ActivityLinks that are causally related.

// Get a context from somewhere, perhaps it's passed in as a parameter
var activityContext = Activity.Current!.Context;

var links = new List<ActivityLink>
{
    new ActivityLink(activityContext)
};

using var anotherActivity =
    MyActivitySource.StartActivity(
        ActivityKind.Internal,
        name: "anotherActivity",
        links: links);

// do some work

Set Activity status

A status can be set on an activity, typically used to specify that an activity has not completed successfully - ActivityStatusCode.Error. In rare scenarios, you could override the Error status with Ok, but don’t set Ok on successfully-completed spans.

The status can be set at any time before the span is finished:

using var myActivity = MyActivitySource.StartActivity("SayHello");

try
{
	// do something
}
catch (Exception ex)
{
    myActivity.SetStatus(ActivityStatusCode.Error, "Something bad happened!");
}

Next steps

After you’ve setup automatic instrumentation, you may want to use instrumentation libraries.Instrumentation libraries will automatically instrument relevant libraries you’re using and generate data for things like inbound and outbound HTTP requests and more.

You’ll also want to configure an appropriate exporter to export your telemetry data to one or more telemetry backends.