Prometheus metrics label value inconsistency between Go and Java

[yzhangyext]

Hi Team,
I've noticed a Prometheus label value inconsistency between Go and Java (java-grpc-prometheus):
e.g. In metrics grpc_server_handled_total,
For grpc_type label, Java is uppercase while go is lower case, e.g. "UNARY" vs "unary"
For grpc_code label, Java is uppercase while go is camel case, e.g. "UNKNOWN" vs "Unknown"
Do you think it's a good idea to have them standardized? I personally prefer the uppercase, but I would love to hear your thoughts on this.

[johanbrandhorst]

Hi, thanks for your issue. I don't know that we can change these now unfortunately, it might break existing users. Note that this is just a third party library and you can probably just copy one of the interceptors and change the labels (preserving the license, of course).

[yzhangyext]

I see. In that case, do you think it's a good idea to allow passing in an option to convert these label values to standardized form (upper case)? It would greatly help us grouping metrics between Go and Java services.

[johanbrandhorst]

I suppose we could consider an option. It looks like the logic for this is here:

go-grpc-middleware/providers/prometheus/reporter.go

Line 31 in 3ade00c

r.incrementWithExemplar(r.serverMetrics.serverHandledCounter, string(r.typ), r.service, r.method, code.String())

and here:

go-grpc-middleware/interceptors/reporter.go

Line 16 in 3ade00c

Unary GRPCType = "unary"

. Please make a more concrete proposal for this option (a PR would do) and we can see if it fits well into the code.