Add instrumentation for gRPC on propagating tags and recording gRPC stats

[mayurkale22]

Provide instrumentation for gRPC Client and Server to record gRPC stats. Interceptors should also propagate Tags.

[vigneshtdev]

I would like to help out with this issue. Any pointers or comparison with any existing package would be welcome.

[mayurkale22]

Specs are available here: https://github.com/census-instrumentation/opencensus-specs/blob/master/stats/gRPC.md

Equivalent counterpart in Java: https://github.com/census-instrumentation/opencensus-java/tree/master/contrib/grpc_metrics/src/main/java/io/opencensus/contrib/grpc/metrics

Equivalent counterpart in Go: https://github.com/census-instrumentation/opencensus-go/blob/2269ed7aa5777d1157c9674a6079207a0f32b68a/plugin/ocgrpc/stats_common.go, https://github.com/census-instrumentation/opencensus-go/blob/2269ed7aa5777d1157c9674a6079207a0f32b68a/plugin/ocgrpc/server_metrics.go, https://github.com/census-instrumentation/opencensus-go/blob/2269ed7aa5777d1157c9674a6079207a0f32b68a/plugin/ocgrpc/client_metrics.go

[songy23]

Also see gRPC-Java: CensusStatsModule and CensusTracingModule.

[vigneshtdev]

should i modify opencensus-intrumentation-grpc or create a new package?

[vigneshtdev]

what is equivalent of Stats.getViewManager()(https://github.com/census-instrumentation/opencensus-java/blob/master/contrib/grpc_metrics/src/main/java/io/opencensus/contrib/grpc/metrics/RpcViews.java#L168) in node package?

[mayurkale22]

ViewManager in Java is for registering views for collecting stats. In Node, you can do that using Stats API itself. (example: stats.registerView(view)).

[vigneshtdev]

but there is no way to get views in node package

[mayurkale22]

I think we should add gerView(view) inside Stats API. Something like python or Java. As per my understanding, View Data is the aggregated data for a particular view. Currently in Node, we don't have ViewData concept. For now, we can use getSnapshot(tags: Tags): AggregationData; method to get snapshot of an AggregationData. WDYT?

[vigneshtdev]

@mayurkale22 can you take a look at this: https://gist.github.com/vigneshtdev/c198d964cccbfc05a3a45e8f18a5d87f

[mayurkale22]

@vigneshtdev this is good start, I would suggest following changes.

1. Separate metrics for client and server (client-metrics.ts and server-metrics.ts)
2. Use new Tags API (Update stats, zpages, prometheus packages with new Tags API #307).
3. I just see constants in gist, do you plan to add record methods (counterpart in go: https://github.com/census-instrumentation/opencensus-go/blob/e16226179d0f7cb82bbdfed8cd824f39bb53e887/plugin/ocgrpc/stats_common.go)?
4. Open a PR for code review.