Telemetry

Introdcution

With both schema registry and client registry now in place, our setup is robust. However, while our queries and mutations are functioning, it's likely that at some point there are still some bugs and performance issues in our application. This is where the importance of telemetry becomes evident.

Preparation

Pick up right where we left off in the previous lesson or start anew with the initial setup located in the src/Chapter10/Lesson3/Begin folder.

Open Telemetry

OpenTelemetry is a collection of APIs, libraries, agents, and instrumentation tools designed to enhance the observability of your application. HotChocolate sends telemetry data using OpenTelemetry protocols. To activate instrumentation in HotChocolate, you need to invoke AddInstrumentation on the IRequestExecutorBuilder.

Banana Cake Pop includes built-in OpenTelemetry support, aiding in diagnostics and understanding application behavior.

To activate OpenTelemetry, simply add the trace exporter in the service defaults (Extensions.cs):

builder.Services.AddOpenTelemetry()
    .WithTracing(tracing =>
    {
        // left out for brevity
        tracing.AddBananaCakePopExporter();
        tracing.AddAspNetCoreInstrumentation()
            .AddHttpClientInstrumentation();
    });

Custom Tracing

While HotChocolate and other libraries provide automatic instrumentation, there are scenarios where you might want to implement custom spans, such as to track execution times. For custom tracing, utilize the ActivitySource class from the System.Diagnostics namespace:

Let's imagine we have a performance issue in the addToBasket mutation and we need to figure out where the bottleneck is.

To create custom traces, you need to use an ActivitySource class from the System.Diagnostics namespace.

public static class Telemetry
{
    public static ActivitySource Source { get; } = new("eShop");
}

We also need to configure .NET to export traces from this source. To do this, extend the tracing configuration in the Extensions.cs file located in ServiceDefaults:

tracing.AddSource("eShop");

This setup allows you to start a new span in services, such as the basket service, to track the serialization time of the basket:

using var activity = Telemetry.Source.StartActivity();
activity?.AddTag("basket.customerId", basket.CustomerId);

Configure OpenTelemetry

Using OpenTelemetry comes with a performance cost. You should decide how much telemetry data you want to collect during runtime. This involves specifying which scopes to trace and which to ignore.

To see the available configurations, you can add this setup in your application:

builder.AddInstrumentation(x =>
{
    x.RequestDetails = RequestDetails.All;
    x.Scopes = ActivityScopes.All;
});

Tasks

1. Follow the instructions above to enable OpenTelemetry in your application.
2. Make a request and track it using the OpenTelemetry dashboard.