Add metrics to ASP.NET Core

[JamesNK]

This PR contains several changes:

• Prototype for System.Diagnostics.Metrics integration with DI (plan is for a new Microsoft.Extensions.Metrics package)
  • This is providing value by making metrics testable but isn't publically available. The temporary workaround is to put types in ASP.NET Core, make them internal, then use InternalsVisibleTo. An alternative idea could be to put these types in a new assembly and keep it internal by not publishing ref pack, but that's more work, and this is just a temporary message.
  • The DI API surface might change, but I expect reacting to the public API won't be a big task.
• Adding metrics to ASP.NET Core. This means adding metrics to places that have event counters today. There is an issue that specifies all the counters added in ASP.NET Core here: ASP.NET Core metrics #47536
  • Add metrics to HTTP hosting. Two new public APIs are used here:
    • IHttpMetricsTagsFeature. API issue: Add IHttpMetricsTagsFeature and IConnectionMetricsTagsFeature #47493
    • IRouteDiagnosticsMetadata. API issue: Add IRouteDiagnosticsMetadata #47492
  • Add metrics to Kestrel. One new public API is used here:
    • IConnectionMetricsTagsFeature. API issue: Add IHttpMetricsTagsFeature and IConnectionMetricsTagsFeature #47493
  • Add metrics to SignalR.

[noahfalk]

Some hopefully useful comments inline. I was more paying attention to the overall patterns and not giving too much thought to what particular metrics/dimensions ASP.NET should have at this point.

[danmoseley]

cc @tarekgh

[JamesNK]

cc @Tratcher @noahfalk @davidfowl

[tarekgh]

I am planning to look at this PR later. Just didn't get a chance yet :-)

[noahfalk]

Coming together 👍 Probably my biggest open question at this point is what guidance/helpers we can offer to make testing as simple as possible.

[davidfowl]

Did you run any tech empower benchmarks?

[JamesNK]

Did you run any tech empower benchmarks?

PlaintextTechEmpower microbenchmark.

[ghost]

@JamesNK, this change will be considered for inclusion in the blog post for the release it'll ship in. Nice work!

Please ensure that the original comment in this thread contains a clear explanation of what the change does, why it's important (what problem does it solve?), and, if relevant, include things like code samples and/or performance numbers.

This content may not be exactly what goes into the blog post, but it will help the team putting together the announcement.

Thanks!