Configure global observation registry

[cfredri4]

This change configures the global observation registry.

Same as is done for the metric registry, but for the observation registry.

[jonatan-ivanov]

What is your use-case?
I don't think it is a good idea to use the global (meter or) observation registry, you should rather inject it.

[cfredri4]

The use case is convenience. It's very convenient to just do Observations.getGlobalRegistry() instead of injecting the registry.
That's why the global registry exists in the first place I assume? And since it does exist, I would intuitively expect Spring Boot to configure it just like is done for metrics.

[jonatan-ivanov]

The use case is convenience. It's very convenient to just do Observations.getGlobalRegistry() instead of injecting the registry.

In my opinion, there is a price you need to pay for doing that (hard to test/configure). This also goes against one of the fundamental concepts of Spring Framework: https://docs.spring.io/spring-framework/reference/core/beans/dependencies/factory-collaborators.html

That's why the global registry exists in the first place I assume? And since it does exist, I would intuitively expect Spring Boot to configure it just like is done for metrics.

The global meter registry predates me and I think maybe it was partly created for this reason (I think largely not) but it would be a wrong assumption for the global observation registry. If I remember correctly, it was created because it was impossible to inject components into some custom components of Netty. If you check its javadoc, it says: "For use especially in places where dependency injection of ObservationRegistry is not possible".

[snicoll]

Thanks @jonatan-ivanov for the review. Closing a result.

[cfredri4]

In my opinion, there is a price you need to pay for doing that (hard to test/configure). This also goes against one of the fundamental concepts of Spring Framework: https://docs.spring.io/spring-framework/reference/core/beans/dependencies/factory-collaborators.html

Sure, but that price is - in many simple cases like mine and I would assume many others - completely insignificant.
I don't need or want to care about the observation registry. There is no testing or configuration of the registry or observations. There is one registry and my services does not/should not care about its details; Spring Boot configures it and it just works.

If I remember correctly, it was created because it was impossible to inject components into some custom components of Netty. If you check its javadoc, it says: "For use especially in places where dependency injection of ObservationRegistry is not possible".

But then for those cases, shouldn't Spring be configuring the global registry to allow such use?
(then you can look away while I and others "abuse" it for convenience. 🫣)