README.md

Prometheus Exporter AspNetCore for OpenTelemetry .NET

An OpenTelemetry Prometheus exporter for configuring an ASP.NET Core application with an endpoint for Prometheus to scrape.

Prerequisite

• Get Prometheus

Steps to enable OpenTelemetry.Exporter.Prometheus.AspNetCore

Step 1: Install Package

dotnet add package --prerelease OpenTelemetry.Exporter.Prometheus.AspNetCore

Step 2: Configure OpenTelemetry MeterProvider

• When using OpenTelemetry.Extensions.Hosting package on .NET 6.0+:

  services.AddOpenTelemetryMetrics(builder =>
  {
      builder.AddPrometheusExporter();
  });

• Or configure directly:

  Call the MeterProviderBuilder.AddPrometheusExporter extension to register the Prometheus exporter.

  var meterProvider = Sdk.CreateMeterProviderBuilder()
      .AddPrometheusExporter()
      .Build();
  builder.Services.AddSingleton(meterProvider);

Step 3: Configure Prometheus Scraping Endpoint

• Register Prometheus scraping middleware using the UseOpenTelemetryPrometheusScrapingEndpoint extension:

  public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
  {
      app.UseOpenTelemetryPrometheusScrapingEndpoint();
      app.UseRouting();
      app.UseEndpoints(endpoints =>
      {
          endpoints.MapControllers();
      });
  }

  Overloads of the UseOpenTelemetryPrometheusScrapingEndpoint extension are provided to change the path or for more advanced configuration a predicate function can be used:

  public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
  {
      app.UseOpenTelemetryPrometheusScrapingEndpoint(
          context => context.Request.Path == "/internal/metrics"
              && context.Connection.LocalPort == 5067);
      app.UseRouting();
      app.UseEndpoints(endpoints =>
      {
          endpoints.MapControllers();
      });
  }

Configuration

The PrometheusExporter can be configured using the PrometheusExporterOptions properties.

ScrapeEndpointPath

Defines the path for the Prometheus scrape endpoint for the middleware registered by UseOpenTelemetryPrometheusScrapingEndpoint. Default value: "/metrics".

ScrapeResponseCacheDurationMilliseconds

Configures scrape endpoint response caching. Multiple scrape requests within the cache duration time period will receive the same previously generated response. The default value is 300. Set to 0 to disable response caching.

Troubleshooting

This component uses an EventSource with the name "OpenTelemetry-Exporter-Prometheus" for its internal logging. Please refer to SDK troubleshooting for instructions on seeing these internal logs.

References

• OpenTelemetry Project
• Prometheus