Add Metrics for Blazor

[danroth27]

We should continue the work we started in .NET 8 of adding Metrics to ASP.NET Core by defining and implementing Metrics for Blazor.

• [Pre5] New Blazor metrics AspNetCore.Docs#35278
• Blazor - rendering metrics and tracing #61609

[ghost]

Thanks for contacting us.

We're moving this issue to the .NET 9 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[javiercn]

See https://learn.microsoft.com/en-us/dotnet/core/diagnostics/metrics-instrumentation for how to create metrics.
See https://learn.microsoft.com/en-us/aspnet/core/log-mon/metrics/metrics?view=aspnetcore-9.0#create-custom-metrics for details on how to do it on ASP.NET Core.
See an example on how to add metrics 34d37ec

When defining metrics, we need to take into account https://learn.microsoft.com/en-us/dotnet/core/diagnostics/metrics-instrumentation#best-practices-4

Our goal here is to define things that will help people understand what's going on the server in order to take action. Based on that here are some things that are interesting to track.

• Number of active circuits.
  • Tells you how many active users are connected.
• Average renders per second:
  • Tells you how much rendering activity is happening across sessions.
• Average interaction to next render
  • Tells the average responsiveness of sessions

We might not be able to collect information on a per-circuit basis, which we might want to do through other mechanisms like activities or ETW.