AspNetCore.SignalR.OpenTelemetry

This is an Instrumentation Library, which instruments ASP.NET Core SignalR and collect traces about SignalR hub method invocations.

Table of Contents

• Install
• Usage
  • Exception Handling
  • Filter
• Example
• Related Work

Install

NuGet: AspNetCore.SignalR.OpenTelemetry

dotnet add package AspNetCore.SignalR.OpenTelemetry

Usage

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSignalR()
    .AddHubInstrumentation(); // <- Add this!

builder.Services.AddOpenTelemetry()
    .ConfigureResource(builder =>
    {
        builder.AddService("AspNetCore.SignalR.OpenTelemetry.Example");
    })
    .WithTracing(providerBuilder =>
    {
        providerBuilder
            .AddAspNetCoreInstrumentation()
            .AddSignalRInstrumentation() // <- Add this!
            .AddOtlpExporter();
    });

Exception Handling

By setting the OnException option, you can override the attributes that this library writes by default. For example, when an exception occurs inside your SignalR hub method, this library sets the otel.status_code attribute to ERROR. However, there are cases where you do not want a specific exception to be ERROR. In that case, you can override the default attribute by setting it as follows.

builder.Services.AddSignalR()
    .AddHubInstrumentation(options =>
    {
        options.OnException = static (activity, exception) =>
        {
            if (exception is HubException)
            {
                activity.SetTag("otel.status_code", "OK");
            }
        };
    });

Filter

If you want to capture traces of specific methods or don't want to capture traces of a specific method, use the Filter option. Filter function that determines whether or not to collect telemetry on a per invocation basis.

builder.Services.AddSignalR()
    .AddHubInstrumentation(options =>
    {
        // same as LINQ's Where method
        options.Filter = context =>
        {
            return context.HubMethodName != "MethodNameOfNotCaptureTraces";
        };
    });

Example

The example code architecture is as follows.

graph LR;
    app[ASP.NET Core Server] --> otelc[OpenTelemetry Collector];
    otelc --> Tempo;
    Grafana --> Tempo;

Loading

The example code can be quickly executed from Visual Studio.

It can also be quickly executed from the CLI.

$ docker compose build
$ docker compose up

• App Server: http://localhost:8080/signalr-dev/index.html
• Grafana: http://localhost:3000/explore

In Grafana, you can see the SignalR method call trace as follows.

Related Work

• nenoNaninu/TypedSignalR.Client
  • C# Source Generator to create strongly typed SignalR clients.
• nenoNaninu/TypedSignalR.Client.TypeScript
  • TypeScript source generator to provide strongly typed SignalR clients by analyzing C# type definitions.
• nenoNaninu/TypedSignalR.Client.DevTools
  • SignalR development tools inspired by SwaggerUI.