Explain difference between OTel agent and Micrometer instrumentations

[marcingrzejszczak]

The suggested approach is to use Micrometer Observation bridge since all Spring projects are using that for instrumentation. One can then use Micrometer OTLP Meter Registry to be OTLP compatible. For Tracing, Micrometer Tracing is suggested with either Brave (once this projects is released in GA) or OTel bridge, in order to be OTLP compliant.

Usage of Agent is discouraged due to various restrictions:

• OpenTelemetry Java Instrumentation project contains multiple alpha JARs (e.g. check the release notes)
• You can't create a native image when using the agent
• Spring Boot OTel configuration is maintained by the Spring Boot team, other auto configurations may not be compatible with Spring Boot supported solutions
• Agent instrumentation is buggy (e.g. issue)

[bclozel]

Thanks Marcin for this suggestion. Rather than trying to compare technologies (we don't usually do that in our reference docs), it would make sense to clear up some points that could confuse developers:

• If your application is using the Observation API, I guess produced metrics and traces won't be exported if you're using the OTel agent?
• If you are using the micrometer bridge, the observation metadata described in Spring reference docs apply (see Spring for GraphQL or Spring Framework). If you're using the OTel agent, its semantics apply instead
• The Spring team does not provide support for the OTel agent in general, you should reach out to the OTel community

Spring projects could also consider echoing this by saying that the metrics/traces described in their reference docs only apply if Micrometer is used, not if a third party instrumentation agent is used.