Getting started with logs - ASP.NET Core

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

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This guide will show you how to get started with OpenTelemetry .NET Logs 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 logs

Install the required OpenTelemetry packages:

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

Update the Program.cs file with the following code:

using OpenTelemetry.Logs;
using OpenTelemetry.Resources;

var builder = WebApplication.CreateBuilder(args);

// For instructional purposes only, disable the default .NET logging providers.
// We remove the console logging provider in this demo to use the verbose
// OpenTelemetry console exporter instead. For most development and production
// scenarios the default console provider works well and there is no need to
// clear these providers.
builder.Logging.ClearProviders();

// Add OpenTelemetry logging provider by calling the WithLogging extension.
builder.Services.AddOpenTelemetry()
    .ConfigureResource(r => r.AddService(builder.Environment.ApplicationName))
    .WithLogging(logging => logging
        /* Note: ConsoleExporter is used for demo purpose only. In production
           environment, ConsoleExporter should be replaced with other exporters
           (for example, OTLP Exporter). */
        .AddConsoleExporter());

var app = builder.Build();

app.MapGet("/", (ILogger<Program> logger) =>
{
    logger.FoodPriceChanged("artichoke", 9.99);

    return "Hello from OpenTelemetry Logs!";
});

app.Logger.StartingApp();

app.Run();

internal static partial class LoggerExtensions
{
    [LoggerMessage(LogLevel.Information, "Starting the app...")]
    public static partial void StartingApp(this ILogger logger);

    [LoggerMessage(LogLevel.Information, "Food `{name}` price changed to `{price}`.")]
    public static partial void FoodPriceChanged(this ILogger logger, string name, double price);
}

Running the application

Run the application:

dotnet run

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

You should see log output in the console similar to:

LogRecord.Timestamp:               2023-09-06T22:59:17.9787564Z
LogRecord.CategoryName:            getting-started-aspnetcore
LogRecord.Severity:                Info
LogRecord.SeverityText:            Information
LogRecord.Body:                    Starting the app...
LogRecord.Attributes (Key:Value):
    OriginalFormat (a.k.a Body): Starting the app...
LogRecord.EventId:                 225744744
LogRecord.EventName:               StartingApp

...

LogRecord.Timestamp:               2023-09-06T23:00:46.1639248Z
LogRecord.TraceId:                 3507087d60ae4b1d2f10e68f4e40784a
LogRecord.SpanId:                  c51be9f19c598b69
LogRecord.TraceFlags:              None
LogRecord.CategoryName:            Program
LogRecord.Severity:                Info
LogRecord.SeverityText:            Information
LogRecord.Body:                    Food `{name}` price changed to `{price}`.
LogRecord.Attributes (Key:Value):
    name: artichoke
    price: 9.99
    OriginalFormat (a.k.a Body): Food `{name}` price changed to `{price}`.
LogRecord.EventId:                 344095174
LogRecord.EventName:               FoodPriceChanged

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

How it works

Replacing default logging providers

For demonstration purposes, the sample clears the default .NET logging providers to better showcase the OpenTelemetry console output:

// For instructional purposes only, disable the default .NET logging providers.
// We remove the console logging provider in this demo to use the verbose
// OpenTelemetry console exporter instead. For most development and production
// scenarios the default console provider works well and there is no need to
// clear these providers.
builder.Logging.ClearProviders();

In a real application, you would typically keep the default providers and add OpenTelemetry alongside them.

Adding OpenTelemetry logging

The application configures OpenTelemetry using the AddOpenTelemetry() extension method:

builder.Services.AddOpenTelemetry()
    .ConfigureResource(r => r.AddService(builder.Environment.ApplicationName))
    .WithLogging(logging => logging
        .AddConsoleExporter());

This code:

  1. Adds OpenTelemetry to the service collection
  2. Configures resource information (like service name)
  3. Sets up logging with the WithLogging() extension
  4. Adds a console exporter to output logs to the console

Using dependency injection for logging

ASP.NET Core provides built-in dependency injection for logging. The sample uses this to inject a logger into the request handler:

app.MapGet("/", (ILogger<Program> logger) =>
{
    logger.FoodPriceChanged("artichoke", 9.99);

    return "Hello from OpenTelemetry Logs!";
});

The ILogger<Program> parameter is automatically injected by the framework, and the log will include the category name “Program”.

Using LoggerMessage source generation

The sample uses compile-time logging source generation for high-performance structured logging:

internal static partial class LoggerExtensions
{
    [LoggerMessage(LogLevel.Information, "Starting the app...")]
    public static partial void StartingApp(this ILogger logger);

    [LoggerMessage(LogLevel.Information, "Food `{name}` price changed to `{price}`.")]
    public static partial void FoodPriceChanged(this ILogger logger, string name, double price);
}

This approach:

  • Delivers better performance than string interpolation.
  • Ensures type safety for log parameters.
  • Produces structured logs with named parameters.
  • Automatically produces EventName on LogRecord.

Learn more


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