interop/xds: Avoid setting unit suffixes

[arjan-bal]

The prometheus exporter changed it's behaviour to add not standard unit suffixes to metrics: open-telemetry/opentelemetry-go#6839. As a result grpc_server_call_started_total becomes grpc_server_call_started_call_total.

From the release notes:

Changed handling of go.opentelemetry.io/otel/exporters/prometheus metric renaming to add unit suffixes when it doesn't match one of the pre-defined values in the unit suffix map.

Similar fix in another project: https://github.com/pomerium/pomerium/pull/5749/files

Tested

Verified by running the otel examples that the units are no longer part of the metric names.

RELEASE NOTES: N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.41%. Comparing base (e1f69d8) to head (f63369e).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8479      +/-   ##
==========================================
- Coverage   82.47%   82.41%   -0.06%     
==========================================
  Files         414      413       -1     
  Lines       40531    40518      -13     
==========================================
- Hits        33429    33394      -35     
- Misses       5743     5762      +19     
- Partials     1359     1362       +3     

see 20 files with indirect coverage changes

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[arjan-bal]

I went through the otel PRs that caused the behaviour change again and I think that there is a bug in gRPCs otel plugin:

grpc-go/stats/opentelemetry/server_metrics.go

Line 57 in ac13172

h.serverMetrics.callStarted = createInt64Counter(metrics.Metrics(), "grpc.server.call.started", meter, otelmetric.WithUnit("call"), otelmetric.WithDescription("Number of server calls started."))

We're specifying the unit as call instead of {call}. Based on the metric naming conventions anything enclosed in curly braces is an annotation and in the absence of a prefix, the unit is 1. The gRPC docs also mention that non-standard units need to be enclosed in curly braces: https://grpc.io/docs/guides/opentelemetry-metrics/#server-instruments.

I believe the correct fix would be to follow the gRPC docs and enclose the required units in {}, however I'm not sure how this would impact existing users of the gRPC otel plugin.

@dfawley @easwars can you comment on this?

[dfawley]

Oh good catch. I would classify that as a bug fix. We should include it in the release notes, but I don't think we have much other option here....

[arjan-bal]

Closing this PR, will open another PR with the correct fix.