feat(tracing): Misc. OTel tracing improvements

[hairyhenderson]

Description

I ran into a few papercuts while setting up tracing with the relay proxy after getting it up and running with #2482, most notably I use OTLP over gRPC rather than the default http/protobuf protocol.

So, this PR adds a few improvements:

• ability to disable with OTEL_SDK_DISABLED=true
• set endpoint with OTEL_EXPORTER_OTLP_ENDPOINT rather than config flag (but config flag is still supported)
• set protocol with OTEL_EXPORTER_OTLP_PROTOCOL (to grpc, for example)
• override service name with OTEL_SERVICE_NAME
• adds more resource attributes by default, including supporting setting from the OTEL_RESOURCE_ATTRIBUTES env var
• adds support for configuring sampling strategy, including with the Jaeger remote sampling protocol
• hooks up the zap logger to OTel's error handling so log messages are formatted nicely, rather than just being logged with the stdlib log.Print

This also fixes a bug where apiServer.Stop() was not properly called. I've also modified the signature to receive a context so we can give the shutdown a 5s timeout.

Closes issue(s)

None directly, but related to #2479

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have updated the documentation (README.md and /website/docs)
• I have followed the contributing guide

[netlify]

✅ Deploy Preview for go-feature-flag-doc-preview canceled.

Name	Link
🔨 Latest commit	1faaed9
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[codecov]

Codecov Report

Attention: Patch coverage is 84.15842% with 16 lines in your changes missing coverage. Please review.

Project coverage is 85.34%. Comparing base (c1c2389) to head (1faaed9).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/relayproxy/api/opentelemetry/otel.go	89.24%	7 Missing and 3 partials ⚠️
cmd/relayproxy/main.go	0.00%	5 Missing ⚠️
cmd/relayproxy/api/server.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2485      +/-   ##
==========================================
+ Coverage   84.81%   85.34%   +0.53%     
==========================================
  Files         100      100              
  Lines        4346     4422      +76     
==========================================
+ Hits         3686     3774      +88     
+ Misses        535      518      -17     
- Partials      125      130       +5     

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[thomaspoignant]

Hey @hairyhenderson thanks a lot for this PR.
I still need to look at it more in details, but I am not a big fan of using os.GetEnv outside of the configuration object.

I would prefer to have all those options in the Config object rather than dealing with env variable directly.

We will still be able to set them via environment variable because we are using knadh/koanf that will allow us to set the values through file and/or environment variable to.

[thomaspoignant]

I've played around with koanf and we could have something like this in the config:

type Config struct {
// ...
	OtelConfig OpenTelemetryConfiguration `mapstructure:"otel" koanf:"otel"`
}


type OpenTelemetryConfiguration struct {
	SDK struct {
		Disabled bool `mapstructure:"disabled" koanf:"disabled"`
	} `mapstructure:"sdk" koanf:"sdk"`
	Exporter struct {
		Otlp struct {
			Endpoint string `mapstructure:"endpoint" koanf:"endpoint"`
			Protocol string `mapstructure:"protocol" koanf:"protocol"`
		} `mapstructure:"otlp" koanf:"otlp"`
	} `mapstructure:"exporter" koanf:"exporter"`
	Service struct {
		Name string `mapstructure:"name" koanf:"name"`
	} `mapstructure:"service" koanf:"service"`
	Traces struct {
		Sampler string `mapstructure:"sampler" koanf:"sampler"`
	} `mapstructure:"sampler" koanf:"sampler"`
	Resource struct {
		Attributes map[string]string `mapstructure:"attributes" koanf:"attributes"`
	} `mapstructure:"resource" koanf:"resource"`
}

This will allow to continue to set all the configuration through environment variable like you do, but at the same time be able to configure directly inside the configuration file also.

What do you think about this idea @hairyhenderson ?
I am happy to help with that if you want.

[hairyhenderson]

What do you think about this idea @hairyhenderson ?

I'm OK either way... It's somewhat more common (in my experience) to see OTel configured through environment variables, but I understand your desire for both modes.

I'm not familiar with koanf so integrating this will take me a bit of time, and I don't have a lot of spare time to spend on this. I'll try to find some time over the next little while to get this updated...

[thomaspoignant]

@hairyhenderson I can do it if you prefer. I am happy to update your PR with the changes if you don't have time.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[thomaspoignant]

@hairyhenderson I have refactored the configuration part.
We can now merge this PR and it will be available in the next version of GO Feature Flag.

[hairyhenderson]

Thanks for this @thomaspoignant!! And sorry I wasn't able to make the changes, things have been busy for me lately 😅

[thomaspoignant]

@hairyhenderson no worries.
Thank you for initiating it.