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Extending the OpenTelemetry .NET SDK

Exporter

OpenTelemetry .NET SDK has provided the following built-in trace exporters:

Custom exporters can be implemented to send telemetry data to places which are not covered by the built-in exporters:

  • Exporters should derive from OpenTelemetry.BaseExporter<Activity> (which belongs to the OpenTelemetry package) and implement the Export method.
  • Exporters can optionally implement the OnShutdown method.
  • Depending on user's choice and load on the application, Export may get called with one or more activities.
  • Exporters will only receive sampled-in and ended activities.
  • Exporters should not throw exceptions from Export and OnShutdown.
  • Exporters should not modify activities they receive (the same activity may be exported again by different exporter).
  • Exporters are responsible for any retry logic needed by the scenario. The SDK does not implement any retry logic.
  • Exporters should avoid generating telemetry and causing live-loop, this can be done via OpenTelemetry.SuppressInstrumentationScope.
class MyExporter : BaseExporter<Activity>
{
    public override ExportResult Export(in Batch<Activity> batch)
    {
        using var scope = SuppressInstrumentationScope.Begin();

        foreach (var activity in batch)
        {
            Console.WriteLine($"Export: {activity.DisplayName}");
        }

        return ExportResult.Success;
    }
}

A demo exporter which simply writes activity name to the console is shown here.

Apart from the exporter itself, you should also provide extension methods as shown here. This allows users to add the Exporter to the TracerProvider as shown in the example here.

Instrumentation Library

TBD

Processor

OpenTelemetry .NET SDK has provided the following built-in processors:

Custom processors can be implemented to cover more scenarios:

  • Processors should inherit from OpenTelemetry.BaseProcessor<Activity> (which belongs to the OpenTelemetry package), and implement the OnStart and OnEnd methods.
  • Processors can optionally implement the OnForceFlush and OnShutdown methods. OnForceFlush should be thread safe.
  • Processors should not throw exceptions from OnStart, OnEnd, OnForceFlush and OnShutdown.
  • OnStart and OnEnd should be thread safe, and should not block or take long time, since they will be called on critical code path.
class MyProcessor : BaseProcessor<Activity>
{
    public override void OnStart(Activity activity)
    {
        Console.WriteLine($"OnStart: {activity.DisplayName}");
    }

    public override void OnEnd(Activity activity)
    {
        Console.WriteLine($"OnEnd: {activity.DisplayName}");
    }
}

A demo processor is shown here.

Sampler

OpenTelemetry .NET SDK has provided the following built-in samplers:

Custom samplers can be implemented to cover more scenarios:

  • Samplers should inherit from OpenTelemetry.Trace.Sampler (which belongs to the OpenTelemetry package), and implement the ShouldSample method.
  • ShouldSample should be thread safe, and should not block or take long time, since it will be called on critical code path.
class MySampler : Sampler
{
    public override SamplingResult ShouldSample(in SamplingParameters samplingParameters)
    {
        return new SamplingResult(SamplingDecision.RecordAndSampled);
    }
}

A demo sampler is shown here.

References