Set up EDOT .NET for ASP.NET applications on .NET Framework

You can use EDOT .NET with ASP.NET applications by registering the OpenTelemetry SDK TelemetryHttpModule.

To get started with the Elastic Distribution of OpenTelemetry .NET, add the Elastic.OpenTelemetry NuGet package reference to your project file:

<PackageReference Include="Elastic.OpenTelemetry" Version="<LATEST>" />

EDOT .NET includes a transitive dependency on the OpenTelemetry SDK, so you do not need to add the OpenTelemetry SDK package to your project directly. However, you can explicitly add the OpenTelemetry SDK as a dependency if you want to opt into newer SDK versions.

For ASP.NET applications, you also need to install the contrib instrumentation library. Add the OpenTelemetry.Instrumentation.AspNet NuGet package reference to your project file:

<PackageReference Include="OpenTelemetry.Instrumentation.AspNet" Version="<LATEST>" />

Next, modify your Web.Config file to add a required HttpModule:

<system.webServer>
   <modules>
      <add
         name="TelemetryHttpModule"
         type="OpenTelemetry.Instrumentation.AspNet.TelemetryHttpModule,
               OpenTelemetry.Instrumentation.AspNet.TelemetryHttpModule"
         preCondition="integratedMode,managedHandler" />
   </modules>
</system.webServer>

Finally, initialize ASP.NET instrumentation in your Global.asax.cs file along with other OpenTelemetry initialization:

using OpenTelemetry;
using OpenTelemetry.Resources;
using System.Web;
using System.Web.Http;
using System.Web.Mvc;
using System.Web.Optimization;
using System.Web.Routing;

namespace AspNetFramework
{
   public class WebApiApplication : HttpApplication
   {
      private OpenTelemetrySdk _sdk;

      protected void Application_Start()
      {
         _sdk = OpenTelemetrySdk.Create(builder => builder
           .WithElasticDefaults()
           .ConfigureResource(r => r.AddService("MyClassicAspNetApp")));

         AreaRegistration.RegisterAllAreas();
         GlobalConfiguration.Configure(WebApiConfig.Register);
         FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
         RouteConfig.RegisterRoutes(RouteTable.Routes);
         BundleConfig.RegisterBundles(BundleTable.Bundles);
      }

      protected void Application_End()
      {
         _sdk?.Dispose();
      }
    }
}

The preceding code:

1. Imports the required types from the OpenTelemetry namespace.
2. Creates an instance of the OpenTelemetrySdk using its factory Create method.
3. Configures the IOpenTelemetryBuilder by passing a lambda.
4. Enables EDOT .NET and its opinionated defaults by calling WithElasticDefaults on the IOpenTelemetryBuilder.
5. Calls ConfigureResource to configure the name for the service.

By default, EDOT .NET uses instrumentation assembly scanning and will detect the OpenTelemetry.Instrumentation.AspNet instrumentation, registering it with the OpenTelemetry SDK. Traces for ASP.NET requests are automatically observed and exported over OTLP without further configuration.

When calling OpenTelemetrySdk.Create a dedicated IServiceCollection and IServiceProvider are created for the SDK and shared by all signals. An IConfiguration is created automatically from environment variables. The recommended method to configure the OpenTelemetry SDK is through environment variables. At a minimum, set the environment variables used to configure the OTLP exporter using any suitable method for your operating system.

"OTEL_EXPORTER_OTLP_ENDPOINT" = "https://{MyServerlessEndpoint}.apm.us-east-1.aws.elastic.cloud:443",
"OTEL_EXPORTER_OTLP_HEADERS" = "Authorization=ApiKey {MyEncodedApiKey}"

For further advice on configuring OpenTelemetry in ASP.NET application visit the OpenTelemetry documentation.