Blazor activity traces get hidden by the SignalR activities for the Blazor component hub

[danroth27]

The new Blazor activity traces get a bit obscured by the SignalR activity traces for the component hub. For example, this is what a Blazor Server based app looks like in the Aspire dashboard:

@pavelsavara @BrennanConroy Is there a way that we hide the SignalR activities for the component hub? The Blazor component hub is really more of an implementation detail of how Blazor works.

[danroth27]

Things look better if I turn off the SignalR activities (tracing.EnableAspNetCoreSignalRSupport = false):

[JamesNK]

I think the answer here is to filter out Blazor's SignalR spans by default. Then someone sees Blazor optimized tracing and has an option to enable Blazor SignalR tracing if they want to, e.g.

.AddAspNetCoreInstrumentation(o =>
{
    // TODO: Improve name.
    o.EnableBlazorSignalRTracing = true;
});

Filtering would be done in ASP.NET Core .NET OTEL SDK bits here.

There are a couple of ways to do it: https://chatgpt.com/share/68414ec5-cbcc-8012-8a3c-b72294bc4f74. I'm not sure which is best.

Can filter based on metadata on SignalR activities/spans:

aspnetcore/src/SignalR/server/Core/src/Internal/DefaultHubDispatcher.cs

Lines 849 to 850 in 4fccb63

	new("rpc.system", "signalr"),
	new("rpc.service", _fullHubName),

Filter when the hub is Microsoft.AspNetCore.Components.Server.ComponentHub. By being specific like this then someone can use SignalR and Blazor in the same app, and see SignalR tracing for their own hubs, and Blazor tracing without ComponentHub for their Blazor app.

[pavelsavara]

I have alternative ideas I would like to discuss:

A) we can make SignalR configurable to enable/disable creation of the span per hub, in our case for ComponentHub. This would require new API for Hub or HubOptions.

B) we can disconnect Blazor activity from the parent in the same way how SignalR disconnects from it's parents. That would make the Blazor top-level span, side by side with SignalR span.

aspnetcore/src/SignalR/server/Core/src/Internal/DefaultHubDispatcher.cs

Lines 398 to 407 in 4fccb63

	// Hub invocation gets its parent from a remote source. Clear any current activity and restore it later.
	var previousActivity = Activity.Current;
	if (previousActivity != null)
	{
	Activity.Current = null;
	}
	// Use hubMethodInvocationMessage.Target instead of methodExecutor.MethodInfo.Name
	// We want to take HubMethodNameAttribute into account which will be the same as what the invocation target is
	var activity = StartActivity(SignalRServerActivitySource.InvocationIn, ActivityKind.Server, connection.OriginalActivity, scope.ServiceProvider, hubMethodInvocationMessage.Target, hubMethodInvocationMessage.Headers, logger);

I think this is preferable to to filtering SignalR spans. I guess they are enabled by default for a reason ?