Exporting OpenTelemetry to Google Cloud with .NET

A while back, Google Cloud Trace support for OpenTelemetry Protocol. This is great news, everyone should support OTLP!

There’s just one issue though. I happen to work with .NET, I could not find anything about it in their documentation.

So here it is, how to use OpenTelemetry.Exporter.OpenTelemetryProtocol to send traces to Google Cloud.

Prerequisites

The documentation is already pretty clear on what permissions are needed, so I won’t go into that.

I will also assume that you know:

  • How to setup credentials for your service, and that you’re already connecting to the platform
  • How to setup OpenTelemetry tracing in your application

Step by step

Let’s start by making sure we have the required nuget packages:

  • Google.Apis.Auth
  • OpenTelemetry.Exporter.OpenTelemetryProtocol
  • OpenTelemetry.Instrumentation.AspNetCore

Then, we need to setup resources for your service when adding OpenTelemetry to your service collection.

You will need at minimum:

  • The name of your service
  • A GCP project ID where to send the traces
.ConfigureResource(resource => resource
    .AddService(serviceName: builder.Environment.ApplicationName) 
    .AddAttributes([KeyValuePair.Create<string, object>("gcp.project_id", "<YOUR PROJECT ID>")]))

Finally that, we setup the OTLP exporter, while connecting the Google Credential to set the proper Authorization header. Use the https://telemetry.googleapis.com endpoint, and create a DelegatingHandler from the Google credential instance.

.AddOtlpExporter(options =>
{
    options.Endpoint = new Uri("https://telemetry.googleapis.com"); // This should be the same for most folks
    options.HttpClientFactory = () =>
    {
        return new HttpClient(credential.ToDelegatingHandler(new HttpClientHandler())); // A DelegatingHandler requires an inner handler, this is why we have a new HttpClientHandler.
    };
});

And that’s pretty much it!

Putting it all together

Here’s a complete example.

using Google.Apis.Auth.OAuth2;
using Google.Apis.Http;
using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

var builder = WebApplication.CreateBuilder(args);

var credential = GoogleCredential.GetApplicationDefault();
var scopedCredential = credential.CreateScoped("https://www.googleapis.com/auth/cloud-platform"); // Not purely required, but can be useful to limit the token scopes

builder.Services.AddOpenTelemetry()
    .ConfigureResource(resource => resource
        .AddService(serviceName: builder.Environment.ApplicationName) 
        .AddAttributes([KeyValuePair.Create<string, object>("gcp.project_id", "<YOUR PROJECT ID>")]))
    .WithTracing(tracing => tracing
        .AddAspNetCoreInstrumentation()
        .AddOtlpExporter(options =>
        {
            options.Endpoint = new Uri("https://telemetry.googleapis.com");
            options.HttpClientFactory = () =>
            {
                return new HttpClient(scopedCredential.ToDelegatingHandler(new HttpClientHandler()));
            };
        }));

var app = builder.Build();

app.MapGet("/", () => "Hello World!");

app.Run();

Troubleshooting

Not seeing anything in Google Trace? Enable OpenTelemetry diagnostics, the answer is likely in there.