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ASP.NET Core Instrumentation for OpenTelemetry .NET

This is an Instrumentation Library, which instruments ASP.NET Core and collect metrics and traces about incoming web requests. This instrumentation also collects traces from incoming gRPC requests using Grpc.AspNetCore.

Note: This component is based on the OpenTelemetry semantic conventions for metrics and traces. These conventions are Experimental, and hence, this package is a pre-release. Until a stable version is released, there can be breaking changes. You can track the progress from milestones.

Steps to enable OpenTelemetry.Instrumentation.AspNetCore

Step 1: Install Package

Add a reference to the OpenTelemetry.Instrumentation.AspNetCore package. Also, add any other instrumentations & exporters you will need.

dotnet add package --prerelease OpenTelemetry.Instrumentation.AspNetCore

Step 2: Enable ASP.NET Core Instrumentation at application startup

ASP.NET Core instrumentation must be enabled at application startup. This is typically done in the ConfigureServices of your Startup class. Both examples below enables OpenTelemetry by calling AddOpenTelemetry() on IServiceCollection. This extension method requires adding the package OpenTelemetry.Extensions.Hosting to the application. This ensures instrumentations are disposed when the host is shutdown.

Traces

The following example demonstrates adding ASP.NET Core instrumentation with the extension method WithTracing() on OpenTelemetryBuilder. then extension method AddAspNetCoreInstrumentation() on TracerProviderBuilder to the application. This example also sets up the Console Exporter, which requires adding the package OpenTelemetry.Exporter.Console to the application.

using Microsoft.Extensions.DependencyInjection;
using OpenTelemetry.Trace;

public void ConfigureServices(IServiceCollection services)
{
    services.AddOpenTelemetry()
        .WithTracing(builder => builder
            .AddAspNetCoreInstrumentation()
            .AddConsoleExporter());
}

Metrics

The following example demonstrates adding ASP.NET Core instrumentation with the extension method WithMetrics() on OpenTelemetryBuilder then extension method AddAspNetCoreInstrumentation() on MeterProviderBuilder to the application. This example also sets up the Console Exporter, which requires adding the package OpenTelemetry.Exporter.Console to the application.

using Microsoft.Extensions.DependencyInjection;
using OpenTelemetry.Metrics;

public void ConfigureServices(IServiceCollection services)
{
    services.AddOpenTelemetry()
        .WithMetrics(builder => builder
            .AddAspNetCoreInstrumentation()
            .AddConsoleExporter());
}

List of metrics produced

The instrumentation is implemented based on metrics semantic conventions. Currently, the instrumentation supports the following metric.

Name	Instrument Type	Unit	Description
`http.server.duration`	Histogram	`ms`	Measures the duration of inbound HTTP requests.

Advanced configuration

This instrumentation can be configured to change the default behavior by using AspNetCoreInstrumentationOptions, which allows adding Filter, Enrich as explained below.

// TODO: This section could be refined. When used with OpenTelemetry.Extensions.Hosting, all configurations to AspNetCoreInstrumentationOptions can be done in the ConfigureServices method of you applications Startup class as shown below.

// Configure
services.Configure<AspNetCoreInstrumentationOptions>(options =>
{
    options.Filter = (httpContext) =>
    {
        // only collect telemetry about HTTP GET requests
        return httpContext.Request.Method.Equals("GET");
    };
});

services.AddOpenTelemetry()
    .WithTracing(builder => builder
        .AddAspNetCoreInstrumentation()
        .AddConsoleExporter());

Filter

This instrumentation by default collects all the incoming http requests. It allows filtering of requests by using the Filter function in AspNetCoreInstrumentationOptions. This defines the condition for allowable requests. The Filter receives the HttpContext of the incoming request, and does not collect telemetry about the request if the Filter returns false or throws exception.

The following code snippet shows how to use Filter to only allow GET requests.

services.AddOpenTelemetry()
    .WithTracing(builder => builder
        .AddAspNetCoreInstrumentation((options) => options.Filter = httpContext =>
        {
            // only collect telemetry about HTTP GET requests
            return httpContext.Request.Method.Equals("GET");
        })
        .AddConsoleExporter());

It is important to note that this Filter option is specific to this instrumentation. OpenTelemetry has a concept of a Sampler, and the Filter option does the filtering after the Sampler is invoked.

Enrich

This instrumentation library provides EnrichWithHttpRequest, EnrichWithHttpResponse and EnrichWithException options that can be used to enrich the activity with additional information from the raw HttpRequest, HttpResponse and Exception objects respectively. These actions are called only when activity.IsAllDataRequested is true. It contains the activity itself (which can be enriched) and the actual raw object.

The following code snippet shows how to enrich the activity using all 3 different options.

services.AddOpenTelemetry()
    .WithTracing(builder => builder
        .AddAspNetCoreInstrumentation(o =>
        {
            o.EnrichWithHttpRequest = (activity, httpRequest) =>
            {
                activity.SetTag("requestProtocol", httpRequest.Protocol);
            };
            o.EnrichWithHttpResponse = (activity, httpResponse) =>
            {
                activity.SetTag("responseLength", httpResponse.ContentLength);
            };
            o.EnrichWithException = (activity, exception) =>
            {
                activity.SetTag("exceptionType", exception.GetType().ToString());
            };
        }));

Processor, is the general extensibility point to add additional properties to any activity. The Enrich option is specific to this instrumentation, and is provided to get access to HttpRequest and HttpResponse.

RecordException

This instrumentation automatically sets Activity Status to Error if an unhandled exception is thrown. Additionally, RecordException feature may be turned on, to store the exception to the Activity itself as ActivityEvent.

Troubleshooting

This component uses an EventSource with the name "OpenTelemetry-Instrumentation-AspNetCore" for its internal logging. Please refer to SDK troubleshooting for instructions on seeing these internal logs.

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