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OpenTelemetry .NET API

NuGet NuGet

Installation

dotnet add package OpenTelemetry.Api

Introduction

Application developers and library authors use OpenTelemetry API to instrument their application/library. The API only surfaces necessary abstractions to instrument an application/library. It does not address concerns like how telemetry is exported to a specific telemetry backend, how to sample the telemetry, etc. The API consists of Tracing API, Logging API, Metrics API, Context and Propagation API, and a set of semantic conventions.

Tracing API

Tracing API allows users to generate Spans, which represent a single operation within a trace. Spans can be nested to form a trace tree. Each trace contains a root span, which typically describes the entire operation and, optionally one or more child-spans for its child-operations.

Logging API

OpenTelemetry does not introduce its own API for logging. Instead it recommends to integrate with existing well-known logging libraries for each language. For .NET, the logging API is simply the Microsoft.Extensions.Logging API.

Metrics API

Metrics API allows users to capture measurements about the execution of a computer program at runtime. The Metrics API is designed to process raw measurements, generally with the intent to produce continuous summaries of those measurements.

Warning: OpenTelemetry .NET has a prototype Metrics API implementation only and is not recommended for any production use. The API is expected to change heavily. Please check the Metric support plan.

Introduction to OpenTelemetry .NET Tracing API

.NET runtime had Activity class for a long time, which was meant to be used for tracing purposes and represents the equivalent of the OpenTelemetry Span. OpenTelemetry .NET is reusing the existing Activity and associated classes to represent the OpenTelemetry Span. This means, users can instrument their applications/libraries to emit OpenTelemetry compatible traces by using just the .NET Runtime.

The Activity and associated classes are shipped as part of System.Diagnostics.DiagnosticSource nuget package. Version 5.0.0 of this package contains improvements to Activity class which makes it more closely aligned with OpenTelemetry API specification.

Even though Activity enables all the scenarios OpenTelemetry supports, users who are already familiar with OpenTelemetry terminology may find it easy to operate with that terminology. For instance, StartSpan may be preferred over StartActivity. To help with this transition, the OpenTelemetry.API package has shim classes to wrap around the .NET Activity classes.

The shim exist only in the API. OpenTelemetry SDK for .NET will be operating entirely with Activity only. Irrespective of whether shim classes or Activity is used for instrumentation, the end result would be same. i.e Processors/Exporters see the same data.

The recommended way of instrumenting is by using the .NET Activity API. Users are required to just take dependency on the DiagnosticSource. Adding dependency to OpenTelemetry.API is required only for the following scenarios:

  1. You want to use terminology matching OpenTelemetry spec (Span vs Activity). The shim can be useful for such users. Refer to the comparison of Activity API and OpenTelemetry Tracing API if you want to compare the differences.
  2. Your library performs communication with other libraries/components, and want to access Propagators, to inject and extract context data. Some of the most common libraries requiring this include HttpClient, ASP.NET, ASP.NET Core. This repo already provides instrumentation for these common libraries. If your library is not built on top of these, and want to leverage propagators, follow the Context propagation section.

Instrumenting a library/application with .NET Activity API

Basic usage

As mentioned in the introduction, the instrumentation API for OpenTelemetry .NET is the .NET Activity API. Guidance for instrumenting using this API is documented fully in the TBD(dotnet activity user guide link), but is described here as well.

  1. Install the System.Diagnostics.DiagnosticSource package version 5.0.0 or above to your application or library.

    <ItemGroup>
  <PackageReference
    Include="System.Diagnostics.DiagnosticSource"
    Version="5.0.0"
  />
</ItemGroup>

  2. Create an ActivitySource, providing the name and version of the library/application doing the instrumentation. ActivitySource instance is typically created once and is reused throughout the application/library.

    static ActivitySource activitySource = new ActivitySource(
    "companyname.product.instrumentationlibrary",
    "semver1.0.0");

    The above requires import of the System.Diagnostics namespace.

  3. Use the ActivitySource instance from above to create Activity instances, which represent a single operation within a trace. The parameter passed is the DisplayName of the activity.

    var activity = activitySource.StartActivity("ActivityName");

    If there are no listeners interested in this activity, the activity above will be null. This happens when the final application does not enable OpenTelemetry (or other ActivityListeners), or when OpenTelemetry samplers chose not to sample this activity. Ensure that all subsequent calls using this activity are protected with a null check.

  4. Populate activity with tags following the OpenTelemetry semantic conventions. It is highly recommended to check activity.IsAllDataRequested, before populating any tags which are not readily available. IsAllDataRequested is the same as Span.IsRecording and will be false when samplers decide to not record the activity, and this can be used to avoid any expensive operation to retrieve tags.

    activity?.SetTag("http.method", "GET");
if (activity != null && activity.IsAllDataRequested == true)
{
    activity.SetTag("http.url", "http://www.mywebsite.com");
}

  5. Perform application/library logic.

  6. Stop the activity when done.

    activity?.Stop();

    Alternately, as Activity implements IDisposable, it can be used with a using block, which ensures activity gets stopped upon disposal. This is shown below.

    using (var activity = activitySource.StartActivity("ActivityName")
{
    activity?.SetTag("http.method", "GET");
} // Activity gets stopped automatically at end of this block during dispose.

The above showed the basic usage of instrumenting using Activity. The following sections describes more features.

Activity creation options

Basic usage example above showed how StartActivity method can be used to start an Activity. The started activity will automatically becomes the Current activity. It is important to note that the StartActivity returns null, if no listeners are interested in the activity to be created. This happens when the final application does not enable OpenTelemetry, or when OpenTelemetry samplers chose not to sample this activity.

StartActivity has many overloads to control the activity creation.

  1. ActivityKind

    Activity has a property called ActivityKind which represents OpenTelemetry SpanKind. The default value will be Internal. StartActivity allows passing the ActivityKind while starting an Activity.

    var activity = activitySource.StartActivity("ActivityName", ActivityKind.Server);

  2. Parent using ActivityContext

    ActivityContext represents the OpenTelemetry SpanContext. While starting a new Activity, the currently active Activity is automatically taken as the parent of the new activity being created. StartActivity allows passing explicit ActivityContext to override this behavior.

    var parentContext = new ActivityContext(
    ActivityTraceId.CreateFromString("0af7651916cd43dd8448eb211c80319c"),
    ActivitySpanId.CreateFromString("b7ad6b7169203331"),
    ActivityTraceFlags.None);

var activity = activitySource.StartActivity(
    "ActivityName",
    ActivityKind.Server,
    parentContext);

    As ActivityContext follows the W3C Trace-Context, it is also possible to provide the parent context as a single string matching the traceparent header of the W3C Trace-Context. This is shown below.

    var activity = activitySource.StartActivity(
    "ActivityName",
    ActivityKind.Server,
    "00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01");

  3. Initial Tags

    Tags in Activity represents the OpenTelemetry Span Attributes. Earlier sample showed the usage of SetTag method of Activity to add tags. Refer to the specification for best practices on naming tags. It is also possible to provide an initial set of tags during activity creation, as shown below. Tags provided at activity creation are accessible for Samplers, whereas any tags added using SetTag are not available for samplers.

    var initialTags = new ActivityTagsCollection();

initialTags["com.mycompany.product.mytag1"] = "tagValue1";
initialTags["com.mycompany.product.mytag2"] = "tagValue2";

var activity = activitySource.StartActivity(
    "ActivityName",
    ActivityKind.Server,
    "00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01",
    initialTags);

    The above requires import of the System.Collections.Generic namespace.

  4. Activity Links

    Apart from the parent-child relation, activities can be linked using ActivityLinks which represent the OpenTelemetry Links. The linked activities must be provided during the creation time, as shown below.

    var activityLinks = new List<ActivityLink>();

var linkedContext1 = new ActivityContext(
    ActivityTraceId.CreateFromString("0af7651916cd43dd8448eb211c80319c"),
    ActivitySpanId.CreateFromString("b7ad6b7169203331"),
    ActivityTraceFlags.None);

var linkedContext2 = new ActivityContext(
    ActivityTraceId.CreateFromString("4bf92f3577b34da6a3ce929d0e0e4736"),
    ActivitySpanId.CreateFromString("00f067aa0ba902b7"),
    ActivityTraceFlags.Recorded);

activityLinks.Add(new ActivityLink(linkedContext1));
activityLinks.Add(new ActivityLink(linkedContext2));

var activity = activitySource.StartActivity(
    "ActivityWithLinks",
    ActivityKind.Server,
    default(ActivityContext),
    initialTags,
    activityLinks);

    Note that Activity above is created with default(ActivityContext) parent, which makes it child of implicit Activity.Current or orphan if there is no Current.

Adding Events

It is possible to add events to Activity using the AddEvent method as shown below.

activity?.AddEvent(new ActivityEvent("sample activity event."));

Apart from providing name, timestamp and attributes can be provided by using corresponding overloads of ActivityEvent.

Setting Status

OpenTelemetry defines a concept called Status to be associated with Activity. There is no Status class in .NET, and hence Status is set to an Activity using the following special tags:

otel.status_code is the Tag name used to store the StatusCode, and otel.status_description is the Tag name used to store the optional Description.

Example:

activity?.SetTag("otel.status_code", "ERROR");
activity?.SetTag("otel.status_description", "error status description");

Values for the StatusCode tag must be one of the strings "UNSET", "OK", or "ERROR", which correspond respectively to the enums Unset, Ok, and Error from StatusCode.

If using OpenTelemetry API shim, then you can leverage the SetStatus extension method on Activity as well.

Instrumenting using OpenTelemetry.API Shim

As mentioned in the introduction section, using OpenTelemetry.API Shim is only recommended if you want to use OpenTelemetry terminology like Tracer, Span instead of ActivitySource, Activity.

Follow this code for example usage of this shim.

Context propagation

OpenTelemetry.API must be used to access Propagators API which defines how to extract and inject context across process boundaries. This is typically required if you are not using any of the .NET communication libraries which has instrumentations already available which does the propagation (eg: Asp.Net Core or HttpClient). In such cases, context extraction and propagation is the responsibility of the library itself. An example would be a producer-consumer pattern using some queuing library like RabbitMQ. Follow the messaging example for examples on how to inject and extract context.

References