Log correlation

Learn how to correlate logs with traces in OpenTelemetry .NET

This guide explains how logs can be correlated with traces in OpenTelemetry .NET.

Logging data model support for correlation

The OpenTelemetry Logging Data Model defines fields which allow a log to be correlated with a span (Activity in .NET). The fields TraceId and SpanId allow a log to be correlated to the corresponding Activity.

Automatic correlation in OpenTelemetry .NET

In OpenTelemetry .NET SDK, there is no user action required to enable correlation. The SDK automatically enables logs to Activity correlation by populating the fields TraceId, SpanId, and TraceFlags from the active activity (that is, Activity.Current), if one exists.

Example

Here’s a simple example showing how to emit logs within the context of an active Activity:

using System;
using System.Diagnostics;
using Microsoft.Extensions.Logging;
using OpenTelemetry;
using OpenTelemetry.Logs;
using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

// Create a logger factory with OpenTelemetry
using var loggerFactory = LoggerFactory.Create(builder =>
{
    builder.AddOpenTelemetry(options =>
    {
        options.AddConsoleExporter();
    });
});

// Create a tracer provider
using var tracerProvider = Sdk.CreateTracerProviderBuilder()
    .AddSource("MyCompany.MyProduct.MyLibrary")
    .AddConsoleExporter()
    .Build();

// Get a logger instance
var logger = loggerFactory.CreateLogger<Program>();

// Create an activity source
var activitySource = new ActivitySource("MyCompany.MyProduct.MyLibrary");

// Start an activity
using (var activity = activitySource.StartActivity("SayHello"))
{
    // Log within the activity context
    logger.FoodPriceChanged("artichoke", 9.99);
}

// Define extension methods for structured logging
internal static partial class LoggerExtensions
{
    [LoggerMessage(LogLevel.Information, "Food `{name}` price changed to `{price}`.")]
    public static partial void FoodPriceChanged(this ILogger logger, string name, double price);
}

Running the application will show the following output on the console:

LogRecord.Timestamp:               2024-01-26T17:55:39.2273475Z
LogRecord.TraceId:                 aed89c3b250fb9d8e16ccab1a4a9bbb5
LogRecord.SpanId:                  bd44308753200c58
LogRecord.TraceFlags:              Recorded
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

...

Activity.TraceId:            aed89c3b250fb9d8e16ccab1a4a9bbb5
Activity.SpanId:             bd44308753200c58
Activity.TraceFlags:         Recorded
Activity.ActivitySourceName: MyCompany.MyProduct.MyLibrary
Activity.DisplayName:        SayHello
Activity.Kind:               Internal
Activity.StartTime:          2024-01-26T17:55:39.2223849Z
Activity.Duration:           00:00:00.0361682
...

As you can see, the LogRecord automatically has the TraceId and SpanId fields matching those from the Activity. This happens because the log was created within the context of an active Activity.

In the Getting Started with Console guide, the logging was done outside of an Activity context, so these correlation fields in the LogRecord were not populated.

Web applications

In web applications like ASP.NET Core, all the logs done within the context of a request are automatically correlated to the Activity representing the incoming request, making it easy to find all logs related to a specific request.

Benefits of log correlation

Log correlation provides several benefits:

  1. Unified view: You can see logs and traces together in a unified view in your observability tool.
  2. Context enrichment: Logs are enriched with trace context, making them more informative.
  3. Troubleshooting: Quickly find all logs related to a specific trace when debugging issues.
  4. Performance analysis: Understand what affects the performance of your application.

Learn more


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