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Getting Started with OpenTelemetry .NET Logs in 5 Minutes - ASP.NET Core Application

First, download and install the .NET SDK on your computer.

Create a new web application:

dotnet new web -o aspnetcoreapp
cd aspnetcoreapp

Install the OpenTelemetry.Exporter.Console and OpenTelemetry.Extensions.Hosting packages:

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

Update the Program.cs file with the code from Program.cs.

Run the application (using dotnet run) and then browse to the URL shown in the console for your application (e.g. http://localhost:5000). You should see the logs output from the console:

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:               2023-09-06T22:59:18.0644378Z
LogRecord.CategoryName:            Microsoft.Hosting.Lifetime
LogRecord.Severity:                Info
LogRecord.SeverityText:            Information
LogRecord.Body:                    Now listening on: {address}
LogRecord.Attributes (Key:Value):
    address: http://localhost:5000
    OriginalFormat (a.k.a Body): Now listening on: {address}
LogRecord.EventId:                 14
LogRecord.EventName:               ListeningOnAddress

...

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.

What does the above program do?

The program has cleared the default logging providers then added OpenTelemetry as a logging provider to the ASP.NET Core logging pipeline. OpenTelemetry SDK is then configured with a ConsoleExporter to export the logs to the console for demonstration purpose (note: ConsoleExporter is not intended for production usage, other exporters such as OTLP Exporter should be used instead). In addition, OpenTelemetryLoggerOptions.IncludeScopes is enabled so the logs will include the log scopes. From the console output we can see the log scopes that are coming from the ASP.NET Core framework, and we can see logs from both our logger and the ASP.NET Core framework loggers, as indicated by the LogRecord.CategoryName.

The example has demonstrated the best practice from ASP.NET Core by injecting generic ILogger<T>:

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

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

Following the .NET logging best practice, compile-time logging source generation has been used across the example, which delivers high performance, structured logging, and type-checked parameters:

public static partial class ApplicationLogs
{
    [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);
}

For logs that occur between builder.Build() and app.Run() when injecting a generic ILogger<T> is not an option, app.Logger is used instead:

app.Logger.StartingApp();

Note There are cases where logging is needed before the dependency injection (DI) logging pipeline is available (e.g. before builder.Build()) or after the DI logging pipeline is disposed (e.g. after app.Run()). The common practice is to use a separate logging pipeline by creating a LoggerFactory instance.

Refer to the Getting Started with OpenTelemetry .NET Logs in 5 Minutes - Console Application tutorial to learn more about how to create a LoggerFactory instance and configure OpenTelemetry to work with it.

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