Add metrics instrumentation for google.golang.org/grpc

[fatsheep9146]

Background

google.golang.org/grpc is already instrumented with library go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc, but this library only covers trace.

So this issue will try to complete all the metrics for google.golang.org/grpc which are already defined in https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/semantic_conventions/rpc-metrics.md

Metrics

Instruments

Server

• [x] rpc.server.duration #2700
• [ ] rpc.server.request.size
• [ ] rpc.server.response.size
• [ ] rpc.server.requests_per_rpc
• [ ] rpc.server.responses_per_rpc

Client

• [ ] rpc.client.duration
• [ ] rpc.client.request.size
• [ ] rpc.client.response.size
• [ ] rpc.client.requests_per_rpc
• [ ] rpc.client.responses_per_rpc

Tasks

• Code complete:
  • [ ] Comprehensive unit tests.
  • [ ] End-to-end integration tests.
  • [ ] Tests all passing.
  • [ ] Instrumentation functionality verified.
• Documented
  • [ ] Added to the OpenTelemetry Registry
  • [ ] README included for the module describing high-level purpose.
  • [ ] Complete documentation of all public API including package documentation.
  • [ ] Instrumentation documentation updated.
• Examples
  • [ ] Dockerfile file to build example application.
  • [ ] docker-compose.yml to run example in a docker environment to demonstrate instrumentation.

[dmathieu]

Related: #2782.

[fatsheep9146]

I think this issue is now blocked by #197

[Sovietaced]

Anyone mind if I add a metrics implementation to the client interceptors?

[ash2k]

I think interceptors are going to be deprecated soon and then removed. https://github.com/open-telemetry/opentelemetry-go-contrib/issues/4318, https://github.com/open-telemetry/opentelemetry-go-contrib/issues/4319. Stats handlers are better - it's hard to do metrics with streaming RPCs as that would require wrapping the stream. It's very clean with stats handlers as gRPC just calls its methods.

[Sovietaced]

I think interceptors are going to be deprecated soon and then removed. #4318, #4319. Stats handlers are better - it's hard to do metrics with streaming RPCs as that would require wrapping the stream. It's very clean with stats handlers as gRPC just calls its methods.

Makes sense, thanks.