What is the easiest way to add custom dimensions to default Request Telemetry for App service?

Question

I just leverage default Application Insights logging to log the request telemetry without ANY custom code. The request telemetry looks like this:

timestamp [UTC]     2019-12-19T00:22:10.2563938Z
id                  |a758472d124b6e4688a33b2ad9755f33.b3979544_
name                GET MyMethod [type]
url                 https://xxxx
success             True
resultCode          200
duration            153.2676
performanceBucket   <250ms
itemType            request
customDimensions 
    AppId                           xxxx-xxxx-xxxx-xxxx-xxxxxx
    AspNetCoreEnvironment:          west us
   _MS.ProcessedByMetricExtractors (Name:'Requests', Ver:'1.1')

Now I want to add a new property to customDimensions in Request telemetry, say, correlationId. What is the easiest way to to it? I just want to expend the existing request telemetry, don't want to create new event.

Answer 1

For adding custom dimensions, you can take use of ITelemetryInitializer.

Here is an example for a .NET core web project:

1.Add a class named MyTelemetryInitializer to the project, and the code like below:

public class MyTelemetryInitializer : ITelemetryInitializer
{
    public void Initialize(ITelemetry telemetry)
    {
        var requestTelemetry = telemetry as RequestTelemetry;

        //if it's not a request, just return.
        if (requestTelemetry == null) return;

        if (!requestTelemetry.Properties.ContainsKey("correlationId"))
        {
            requestTelemetry.Properties.Add("correlationId", "id_123456");
        }
    }

 }

2.In Startup.cs -> ConfigureServices method, use the following code:

    public void ConfigureServices(IServiceCollection services)
    {
       //your other code           

        //register the class MyTelemetryInitializer.
        services.AddSingleton<ITelemetryInitializer, MyTelemetryInitializer>();
    }

The test result:

If you're using other programming language, please follow the official doc and use the proper method for ITelemetryInitializer.