add the option to enable server reflection on otlp grpc receiver

[tvaintrob]

Describe the solution you'd like a configuration to enable server reflection on the grpc otlp receiver something like the following:

receivers:
  otlp:
    protocols:
      grpc:
        enable_reflection: true

Describe alternatives you've considered thought about adding a new receiver plugin but seems like the better solution is to add the functionality to the default one

id be happy to implement this one myself and submit a PR

[tigrannajaryan]

Please clarify the purpose of this feature. What does server reflection do?

[jpkrohling]

The biggest advantage is listing the resources a server provides. It allows a tool like grpccurl to be more user-friendly. We'd likely not have this enabled in production, but I can see how this can help debug connectivity and configuration issues.

[kvc0]

I'm trying to write a tool that sends messages directly to opentelemetry collector and I receive this when sending messages via your proto service definition:

(logged by my client - Channel established, request made it to otel collector, this is the response from otel collector)

{ code: Unimplemented, message: "unknown service opentelemetry.proto.metrics_service.MetricsService", metadata: MetadataMap { headers: {"content-type": "application/grpc"} }, source: None }

The very next thing I did to understand what the collector is looking for was to reach for grpcurl's list verb.

➜  ~ grpcurl -plaintext localhost:4317 list                        
Failed to list services: server does not support the reflection API

I still do not know what's wrong.

Here is how I'm running otel:

docker run -p 4317:4317 --name otel --rm otel/opentelemetry-collector

Not supporting reflection at all is quite hostile to those integrating with the collector. I actually thought the missing reflection was a bug!

[AlexDCraig]

Why is this not supported? Would love to be able to grpcurl this thing without it being a huge pain

[brandtkilian]

If that can be of any interest as a workaround, I am using grpcui, then I cloned opentelemetry-proto repository and I am using something along:

grpcui -plaintext -import-path /path/to/opentelemetry-proto/ -proto /path/to/opentelemetry-proto/opentelemetry/proto/collector/metrics/v1/metrics_service.proto 127.0.0.1:{your_otlp_grpc_port}

Then I can craft my export metrics test queries from a web ui.

As a side note, the -plaintext and -proto options of grpcui are really similar to the grpcurl ones so you might be able to replicate that with grpcurl easily.

reflection would be nice to have tho...

[K-MTG]

@brandtkilian, would you be able to share the example export metrics test queries?

I'm getting a undefined is not an object (evaluating 'schema.requestType')