opentelemetry-dotnet/docs/customization.md

Customizing OpenTelemetry .NET

Custom Samplers

You may configure sampler of your choice

TracerProviderSdk.EnableTracerProvider(b => b
    .AddActivitySource(ActivitySourceName)
    .SetSampler(new ProbabilityActivitySampler(0.1))
    .SetResource(Resources.Resources.CreateServiceResource("my-service"))
    .UseZipkinExporter(options => {}));

You can also implement a custom sampler and should subclass ActivitySampler

class MySampler : ActivitySampler
{
    public override string Description { get; } = "my custom sampler";

    public override SamplingResult ShouldSample(in ActivitySamplingParameters samplingParameters)
    {
        bool sampledIn;
        var parentContext = samplingParameters.ParentContext;
        if (parentContext != null && parentContext.IsValid())
        {
            sampledIn = (
                parentContext.TraceFlags & ActivityTraceFlags.Recorded
            ) != 0;
        }
        else
        {
            sampledIn = Stopwatch.GetTimestamp() % 2 == 0;
        }

        return new Decision(sampledIn);
    }
}

Custom Exporters

Tracing

• Exporters should subclass ActivityExporter and implement ExportAsync and ShutdownAsync methods.
• Depending on user's choice and load on the application ExportAsync may get called concurrently with zero or more activities.
• Exporters should expect to receive only sampled-in ended activities.
• Exporters must not throw.
• Exporters should not modify activities they receive (the same activity may be exported again by different exporter).

It's a good practice to make exporter IDisposable and shut it down in IDispose unless it was shut down explicitly. This helps when exporters are registered with dependency injection framework and their lifetime is tight to the app lifetime.

class MyExporter : ActivityExporter, IDisposable
{
    public override Task<ExportResult> ExportAsync(
        IEnumerable<Activity> batch, CancellationToken cancellationToken)
    {
        foreach (var activity in batch)
        {
            Console.WriteLine(
                $"[{activity.StartTimeUtc:o}] " +
                $"{activity.DisplayName} " +
                $"{activity.Context.TraceId.ToHexString()} " +
                $"{activity.Context.SpanId.ToHexString()}"
            );
        }

        return Task.FromResult(ExportResult.Success);
    }

    public override Task ShutdownAsync(CancellationToken cancellationToken)
    {
        return Task.CompletedTask;
    }

    public void Dispose()
    {
        // ...
    }

    protected virtual void Dispose(bool disposing)
    {
        // ...
    }
}

• Users may configure the exporter similarly to other exporters.
• You should also provide additional methods to simplify configuration similarly to UseZipkinExporter extension method.

TracerProviderSdk.EnableTracerProvider(b => b
    .AddActivitySource(ActivitySourceName)
    .UseMyExporter();