Documentation of ObservationRestTemplateCustomizer as replacement of MetricsRestTemplateCustomizer

[MahatmaFatalError]

This issue #32484 with commit eac50a8#diff-4cdef5c5ee8ef10a5d751cbb07a000805bac055f8fa8a1620b0e219826e3eb74 removed org.springframework.boot.actuate.metrics.web.client.MetricsRestTemplateCustomizer and introduced org.springframework.boot.actuate.metrics.web.client.ObservationRestTemplateCustomizer. I assume the latter is a drop-in replacement, I don't know.

IMHO this breaking change should be documented, maybe https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-3.0-Migration-Guide or https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-3.0-Release-Notes.

[GirishSrinivas]

Hi,
we are doing the spring boot 3 migrations, and we are using the claas MetricsRestTemplateCustomizer for the restTemplate, we have not see any documentation about this change.
It would be greatly appreciated if you can point us to any documentation for the migration of MetricsRestTemplateCustomizer to ObservationRestTemplateCustomizer

[bclozel]

Can you elaborate on why are you using this customizer in the first place? What type of customization are you applying here? I'm asking this because you are not required to define your own and this should be mostly a transparent change for Boot users.

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[MahatmaFatalError]

@wilkinsona we used

metricsRestTemplateCustomizer.customize(restTemplate);

and now needed to replace it with

observationRestTemplateCustomizer.customize(restTemplate);

to access /actuator/metrics/http.client.requests metrics.

[bclozel]

Given the use case, I'm not sure we need to add much more in the docs. You're not really supposed to use the customizers directly but rather inject a RestTemplateBuilder in your application. I've added a note in the migration wiki still.