Getting started with traces - ASP.NET Core

Learn how to use OpenTelemetry Traces in an ASP.NET Core application

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This guide will show you how to get started with OpenTelemetry .NET Traces in an ASP.NET Core application.

Prerequisites

Creating an ASP.NET Core application

Create a new ASP.NET Core web application:

dotnet new web -o aspnetcoreapp
cd aspnetcoreapp

Adding OpenTelemetry traces

Install the required OpenTelemetry packages:

dotnet add package OpenTelemetry.Exporter.Console
dotnet add package OpenTelemetry.Extensions.Hosting
dotnet add package OpenTelemetry.Instrumentation.AspNetCore

Update the Program.cs file with the following code:

using System.Diagnostics;
using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

var builder = WebApplication.CreateBuilder(args);

// Configure OpenTelemetry with tracing and auto-start.
builder.Services.AddOpenTelemetry()
    .ConfigureResource(resource => resource
        .AddService(serviceName: builder.Environment.ApplicationName))
    .WithTracing(tracing => tracing
        .AddAspNetCoreInstrumentation()
        .AddConsoleExporter());

var app = builder.Build();

app.MapGet("/", () => $"Hello World! OpenTelemetry Trace: {Activity.Current?.Id}");

app.Run();

Running the application

Run the application:

dotnet run

Browse to the URL shown in the console (for example, http://localhost:5000).

You should see trace output in the console similar to:

Activity.TraceId:            c28f7b480d5c7dfc30cfbd80ad29028d
Activity.SpanId:             27e478bbf9fdec10
Activity.TraceFlags:         Recorded
Activity.ActivitySourceName: Microsoft.AspNetCore
Activity.DisplayName:        GET /
Activity.Kind:               Server
Activity.StartTime:          2024-07-04T13:03:37.3318740Z
Activity.Duration:           00:00:00.3693734
Activity.Tags:
    server.address: localhost
    server.port: 5154
    http.request.method: GET
    url.scheme: https
    url.path: /
    network.protocol.version: 2
    user_agent.original: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36
    http.route: /
    http.response.status_code: 200
Resource associated with Activity:
    service.name: getting-started-aspnetcore
    service.instance.id: a388466b-4969-4bb0-ad96-8f39527fa66b
    telemetry.sdk.name: opentelemetry
    telemetry.sdk.language: dotnet
    telemetry.sdk.version: 1.9.0

Congratulations! You are now collecting traces using OpenTelemetry in your ASP.NET Core application.

How it works

OpenTelemetry registration

The application registers OpenTelemetry services using the dependency injection container provided by ASP.NET Core:

builder.Services.AddOpenTelemetry()
    .ConfigureResource(resource => resource
        .AddService(serviceName: builder.Environment.ApplicationName))
    .WithTracing(tracing => tracing
        .AddAspNetCoreInstrumentation()
        .AddConsoleExporter());

This code:

  1. Adds OpenTelemetry to the service collection with AddOpenTelemetry()
  2. Configures a resource with service information using ConfigureResource()
  3. Sets up trace collection with WithTracing()
  4. Adds automatic instrumentation for ASP.NET Core with AddAspNetCoreInstrumentation()
  5. Configures the console exporter to output traces to the console

ASP.NET Core instrumentation

The AddAspNetCoreInstrumentation() method automatically creates traces for HTTP requests, including:

  • Request duration
  • HTTP method, route, and status code
  • Network information
  • User agent

These traces are collected without requiring any additional code in your controllers or middleware.

Accessing the current activity

In OpenTelemetry .NET, the Activity class represents the OpenTelemetry specification’s “Span”. In our example, we access the current Activity to include its ID in the response:

app.MapGet("/", () => $"Hello World! OpenTelemetry Trace: {Activity.Current?.Id}");

This allows you to see the trace ID in the browser and correlate it with the traces in your monitoring system.

Learn more


Última modificación August 12, 2025: Add dotnet docs from /docs folder of opentelemetry-dotnet (#7474) (bb927496)