Having AspectJ and Micrometer on the classpath is not a strong enough signal to enable support for Micrometer observation annotations

[bclozel]

As of #37626, Spring Boot 3.2 auto-configures AspectJ handlers to support observation annotations like @Timed and @Counted with MetricsAspectsAutoConfiguration. Spring Boot 3.3 will expand that for tracing annotations in MicrometerTracingAutoConfiguration.

Right now those auto-configurations are conditional on the presence of Micrometer and AspectJ, but we've found that those aspects are quite broadly applied and can significant startup time difference. While this is a fine feature to support, we should restrict a bit its application to ensure that it's only applied when developers choose to. The Aspectj dependency can come from many use cases and is not a good indicator for applications opting-in for this feature.

We should add a management.observations.annotations.enabled configuration property and introduce it with a default false value. While this changes behavior, we're still early in the 3.2.x generation and this is a impact big enough that we're considering this a bug. We'll make this noteworthy in the release notes.

[DRoppelt]

We'll make this noteworthy in the release notes.

It seems like that might have been forgotten in the release notes? I like this change but have not perceived it as a noteworthy change in the release notes/blog. It does show up under "bugfixes". https://github.com/spring-projects/spring-boot/releases/tag/v3.2.2

I think the notes should be updated to highlight that change better?

[wilkinsona]

Thanks, @DRoppelt. Looks like we missed this during the release. I've added a Noteworthy Changes section to the top of the release notes for 3.2.2.

[DarkAtra]

hey @wilkinsona, just noticed that the release notes are incorrect. It says the property is management.observations.annotations.enabled but the actual name seems to be micrometer.observations.annotations.enabled.

[philwebb]

Thanks @DarkAtra, I've edited the notes.

[wilkinsona]

I think that may be a mistake in the code as we have ObservationProperties with a management.observations prefix.

[bclozel]

My mistake, I've created #39600 to fix that.