feat: implement otlp exporter

[alexandrebrg]

This PR adds the ability to export metrics through OpenTelemetry protocol.

Description

This PR implements a way to use metrics given by OpenFGA. The default behavior is that no metrics are exposed NoopMeter is used.

How OTLP is implemented ?

Metrics export can be either done by gRPC or by HTTP. The endpoint can also be configured. There isn't a lot of parameters implemented as the SDK can contain a lot of breaking changes through time. Moreover, OpenTelemetry SDK can be configured through environment variables (see SDK).

How to test OTLP implementation ?

openfga run --metrics-exporter "otlp" --metrics-endpoint "localhost:9000" --metrics-protocol "grpc"

(An Otel Collector can be installed easily with opentelemetry-collector-contrib/examples/demo)

References

#254

Review Checklist

• I have clicked on "allow edits by maintainers".
• (Pending) I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: AlexandreBrg / name: Alexandre Burgoni (2a7cc5f, 23c65d5)

[craigpastro]

Wow! Thanks for this great PR. The OpenFGA team is on vacation this week, but we’ll try to get around to reviewing this early next week. Thanks again for the contribution!

[codecov-commenter]

Codecov Report

Base: 84.68% // Head: 84.54% // Decreases project coverage by -0.14% ⚠️

Coverage data is based on head (7c79a3e) compared to base (e96509a).
Patch coverage: 62.50% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #360      +/-   ##
==========================================
- Coverage   84.68%   84.54%   -0.15%     
==========================================
  Files          84       84              
  Lines       13834    13895      +61     
==========================================
+ Hits        11716    11747      +31     
- Misses       1736     1759      +23     
- Partials      382      389       +7     

Impacted Files	Coverage Δ
server/commands/check.go	87.50% <ø> (-0.53%)	⬇️
cmd/run.go	51.54% <31.81%> (-0.59%)	⬇️
pkg/telemetry/metrics.go	76.92% <76.00%> (-23.08%)	⬇️
server/commands/check_utils.go	97.60% <0.00%> (-1.44%)	⬇️
storage/mysql/mysql.go	69.21% <0.00%> (-0.53%)	⬇️
storage/memory/memory.go	93.97% <0.00%> (+0.40%)	⬆️

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[jon-whit]

@alexandrebrg thanks for contributing 👍 We've had telemetry on the todo list for a hot-minute.

I like the approach you've taken here, and we'd love to move forward with your contribution. However, we'd like to minimize the maintenance footprint of the OpenTelemetry integration in OpenFGA. For this reason, we'd prefer to support a single OpenTelemetry exporter and encourage the community to use the OTEL Collector if they need to collect and transform to an alternative format (e.g. prometheus, jaeger, etc..).

Would you mind repurposing this PR to expose only the otlp exporter ?

[alexandrebrg]

@alexandrebrg thanks for contributing 👍 We've had telemetry on the todo list for a hot-minute.

I like the approach you've taken here, and we'd love to move forward with your contribution. However, we'd like to minimize the maintenance footprint of the OpenTelemetry integration in OpenFGA. For this reason, we'd prefer to support a single OpenTelemetry exporter and encourage the community to use the OTEL Collector if they need to collect and transform to an alternative format (e.g. prometheus, jaeger, etc..).

Would you mind repurposing this PR to expose only the otlp exporter ?

Thank you! I'll update the PR accordingly with your request 😄

[craigpastro]

Hi @alexandrebrg, great PR! Thank you for this work. I left a couple of very small comments. I suppose the big issue is the change from gauge to counter. I don't have an opinion yet, but I'll form one and join the conversation there.

Thanks again!

[alexandrebrg]

Hello, I applied all of your reviews, thank you for the time given on this PR :)

[craigpastro]

Thank you for your contribution @alexandrebrg 🙌 This is great!

I added host and runtime metrics to your PR just so we can get it in quickly.

Thanks again!

[rhamzeh]

@alexandrebrg, we're considering replacing our OpenTelemetry metrics for Prometheus metrics. @jon-whit expanded more on our reasoning here: #514 (comment)

We wanted to check in with you and get your opinion on this change, please feel free to add any comments on @jon-whit's PR here