Metrics in .NET with OpenTelemetry

In the previous article, I wrote about Distributed Tracing with OpenTelementry. Now, let’s write about Metrics.

OpenTelementry .NET Metrics API

The .NET runtime contains most of Metric API, that allows applications to emit OpenTelemetry metrics using the standard .NET runtime.

Metrics

Use the Meter class, which is responsible for creating metric instruments to create manual metrics from the System.Diagnostics.DiagnosticSource nuget package.

 static readonly Meter meter = new("serviceName", "1.0");

The default, there is no listener to meters; they need to be explicit configured into the MeterProvider. The MeterProvider is the entry point to the configuration of all Meter’s and their instrumentation.

It’s not recommended to initialize the instrument for every metric execution. Create a (static) wrapper over metrics.

Initialize

Initialize some kinds of instruments - Counter, Gauge, Histogram, …

public static class ApplicationMetrics
{
    private static readonly Meter meter = new Meter("applicationName", "1.0.0");
    private static readonly Counter<int> applicationCounter = meter.CreateCounter<int>("applicationCounter");

    public static void IncreaceCounter() => applicationCounter.Add(1);
}

Usage

public void SomeMethod()
{
    // Code
    ApplicationMetrics.IncreaceCounter();
    // Code
}

Aggregation

It provides a way to aggregate large number of measurements. More detailed description here.

Views

It provides a way to customize the metrics output - which metric instruments are to be processed, which attributes report. More detailed description here.

Configure OpenTelemetry

As tracing, also metrics are part of the OpenTelemetry.Extensions.Hosting nuget package.

builder.Services.AddOpenTelemetry()
    .WithMetrics(metrics =>
    {
        metrics.SetResourceBuilder(ResourceBuilder.CreateDefault()
                    .AddService("serviceName"))
                .AddMeter("serviceName"); // Configure meter to listen
    });

Instrumentations

Metrics instruments must be registered by AddMeter("meterName") to MeterProvider. There exist some build-in Meter’s to instrument ASP.NET application Microsoft.AspNetCore.Hosting, Microsoft.AspNetCore.Server.Kestrel, System.Net.Http.

To instrument the application’s runtime (ram, cpu, gc,…) install OpenTelemetry.Instrumentation.Runtime and configure it by AddRuntimeInstrumentation.

builder.Services.AddOpenTelemetry()
    .WithMetrics(metrics =>
    {
        metrics.SetResourceBuilder(ResourceBuilder.CreateDefault()
                    .AddService("serviceName"))
                .AddMeter("serviceName"); // Configure meter to listen
                .AddMeter("Microsoft.AspNetCore.Hosting", "Microsoft.AspNetCore.Server.Kestrel", "System.Net.Http");
                .AddRuntimeInstrumentation()
    });

Exporters

There are several ways to export metrics to backends - OTLP, Console, and Prometheus in the namespace of the OpenTelemetry.Exporter.NAME nuget package.

To enable OTLP exporter for all signals, there is exists an extension UseOtlpExporter.

builder.Services.AddOpenTelemetry()
    .UseOtlpExporter();