gRPC health checking against a predefined proto

[irfn]

Feature request.
Envoy could come up with a standard for grpc health-check eg:
https://github.com/grpc/grpc/blob/master/doc/health-checking.md

syntax = "proto3";

package grpc.health.v1;

message HealthCheckRequest {
  string service = 1;
}

message HealthCheckResponse {
  enum ServingStatus {
    UNKNOWN = 0;
    SERVING = 1;
    NOT_SERVING = 2;
  }
  ServingStatus status = 1;
}

service Health {
  rpc Check(HealthCheckRequest) returns (HealthCheckResponse);
}

Anyone wanting to do this would have to implement this and configure the check to be grpc.

[irfn]

@mattklein123 are you ok adding grpc dependencies to achieve this. If not then any suggestions?

[mattklein123]

We won't take the gRPC runtime as a dependency, mostly do to lack of ability to control threading and transport. Instead, we should do the following:

1. Define a .proto gRPC HC API (this should be proposed here so community can discuss). This would get added to the Envoy repo and compiled like this proto: https://github.com/lyft/envoy/blob/master/source/common/ratelimit/ratelimit.proto
2. Use rpc_channel_impl like for ratelimit to call HC API
3. Define new gRPC HC checker type here: https://github.com/lyft/envoy/blob/master/source/common/upstream/health_checker_impl.h

This is probably an ~1 week item for someone not familiar with the code but is comfortable w/ C++. If you interested feel feel free, but please keep us in the loop so that we can make sure you are on the right track.

[irfn]

@mattklein123 i would be interested for sure. ill spend some time understanding the health_checker first.
Would Envoy be supporting streaming grpc in addition to the current unary rpc. Healthchecks would then probably need something like a DRAIN in addition to SERVING, NOT_SERVING.

[mattklein123]

Apparently there is this proto that I didn't know about:
https://github.com/grpc/grpc/blob/master/doc/health-checking.md

So we should use that and define a gRPC http/2 HC type.

[mattklein123]

I think @craffert0 is going to implement this as an onboarding project as there is a place we can make use of this at Lyft and this is a generally useful feature.

@htuch @fengli79 @lizan do you know if the proto listed in the above MD file is hosted anywhere official? Or should we copy into data-plane-api? (That seems not great).

[htuch]

https://github.com/grpc/grpc/blob/master/src/proto/grpc/health/v1/health.proto

[lizan]

I believe https://github.com/grpc/grpc-proto is for proto-only purpose but looks like health.proto is not there.