zPages: rpcz support

[VineethReddy02]

Feature Proposal from @SergeyKanzhelev

zPages is a great practice many organizations and SRE uses for the last line of defence while troubleshooting application issues. zPages aggregate telemetry in-process in a memory buffer and allow to query this informaiton directly from the app. It will be great to design and implement zPages

See some info on zPages: https://opencensus.io/zpages/

Also features in SRE book.

• [ ] Basic project set up.
  • [ ] Create a separate project. Zipkin can be used as an example.
  • [ ] Implement TelemetryProcessor that will receive all span's creation/finish events.
  • [ ] Make sure you can configure processor to receive all spans
• [ ] Basic zPage
  • [ ] Implement HttpListener (as in Prometheus package) that will return an empty html
  • [ ] Hook up telemetry processor and this httpListener. As a prove that those are connected - write the current number of active spans and the "last seen" span information in html output.
• [ ] Specification on zPage output
  • [ ] Take the zPage implemented in OpenCensus as a baseline.
  • [ ] Write down very basic specification on zPage output
    • [ ] Iterate on zPage output. Update specs, implement it in Golang.
    • [ ] Perf benchmarking.
    • [ ] Benchmark individual zPage methods
    • [ ] Benchmark zPage with the multiple simultaneous connections

[jmacd]

One of the useful things you can do with a z-page is link from one active request to an active, remote child request. This is a nice way to find deadlocks and hung requests. It calls for a specification of what z-pages can do and how to form links into a z-page if you know the endpoint you are talking to.

[MrAlias]

Closed with https://github.com/open-telemetry/opentelemetry-go-contrib/pull/894

[burdiyan]

AFAIK, this only implements tracez, but this issue is about supporting rpcz.