ErrorAndSlowRateSamplerProcessor

README.md

Usage:

public static TBuilder ConfigureOpenTelemetry<TBuilder>(this TBuilder builder) where TBuilder : IHostApplicationBuilder
{
    builder.Logging.AddOpenTelemetry(logging =>
    {
        logging.IncludeFormattedMessage = true;
        logging.IncludeScopes = true;
    });

    builder.AddOpenTelemetryExporters()
        .Select(telemetryBuilder => telemetryBuilder
            .WithMetrics(metrics =>
            {
                metrics.AddAspNetCoreInstrumentation()
                    .AddHttpClientInstrumentation()
                    .AddRuntimeInstrumentation();
            })
            .WithTracing(tracing =>
            {
                tracing.AddAspNetCoreInstrumentation()
                    .AddHttpClientInstrumentation()
                    .AddProcessor(new ErrorAndSlowRateSamplerProcessor(
                        predicate: activity => activity.OperationName == "CustomThingy",
                        samplingProbability: builder.Environment.IsProduction() ? 0.02 : 1,
                        maxDurationPredicate: TimeSpan.FromSeconds(1)))
                    .SetSampler(new ParentBasedSampler(
                        rootSampler: new AlwaysOnSampler(),
                        remoteParentNotSampled: new AlwaysOnSampler()));
            }))
        .ToArray();

    return builder;
}

private static IEnumerable<IOpenTelemetryBuilder> AddOpenTelemetryExporters<TBuilder>(this TBuilder builder) where TBuilder : IHostApplicationBuilder
{
    if (!string.IsNullOrWhiteSpace(builder.Configuration["OTEL_EXPORTER_OTLP_ENDPOINT"]))
    {
        yield return builder.Services
            .AddOpenTelemetry()
            .UseOtlpExporter();
    }

    if (!string.IsNullOrWhiteSpace(builder.Configuration["APPLICATIONINSIGHTS_CONNECTION_STRING"]))
    {
        yield return builder.Services
            .AddOpenTelemetry()
            .UseAzureMonitor();
    }
}

ErrorAndSlowRateSamplerProcessor.cs

using System.Diagnostics;
using OpenTelemetry.Trace;

namespace OpenTelemetry;

/// <summary>
/// A high-performance probabilistic processor that samples activities based on a predicate and rate.
/// </summary>
public sealed class ErrorAndSlowRateSamplerProcessor : BaseProcessor<Activity>
{
    private readonly Func<Activity, bool> predicate;
    private readonly TimeSpan maxDurationPredicate;
    private readonly TraceIdRatioBasedSampler sampler;

    /// <summary>
    /// Initializes a new instance of the <see cref="ErrorAndSlowRateSamplerProcessor"/> class.
    /// </summary>
    /// <param name="predicate">The predicate to determine if an activity should be sampled.</param>
    public ErrorAndSlowRateSamplerProcessor(Func<Activity, bool> predicate, double samplingProbability, TimeSpan maxDurationPredicate)
    {
        ArgumentNullException.ThrowIfNull(predicate);

        this.predicate = predicate;
        this.maxDurationPredicate = maxDurationPredicate;
        this.sampler = new TraceIdRatioBasedSampler(samplingProbability);
    }

    /// <inheritdoc/>
    public override void OnStart(Activity? data)
    {
        if (data is null || !predicate(data))
        {
            return;
        }

        var samplingParameters = new SamplingParameters(
            new ActivityContext(
                data.TraceId,
                data.SpanId,
                data.ActivityTraceFlags
            ),
            data.TraceId,
            data.DisplayName,
            data.Kind,
            data.TagObjects,
            data.Links
        );

        var result = sampler.ShouldSample(in samplingParameters);
        data.IsAllDataRequested = result.Decision is SamplingDecision.RecordAndSample;
        data.ActivityTraceFlags = result.Decision is SamplingDecision.RecordAndSample
            ? ActivityTraceFlags.Recorded
            : ActivityTraceFlags.None;
    }

    /// <inheritdoc/>
    public override void OnEnd(Activity? data)
    {
        if (data is not null && predicate(data) && (data.Status is ActivityStatusCode.Error || data.Duration > maxDurationPredicate))
        {
            data.IsAllDataRequested = true;
            data.ActivityTraceFlags = ActivityTraceFlags.Recorded;
        }
    }
}