Autoconfigure RabbitMQ Java Client metrics

[acogoluegnes]

Enable RabbitMQ Java Client metrics collection if RabbitMQ Java Client 4.0 and Dropwizard Metrics are on the classpath. Configuration flag can also enable/disable (default is to enable).

spring-projects/spring-amqp#507 needs to be merged first.

Fixes #7498

[philwebb]

We'll need to consider the Rabbit client 4.0 upgrade (#7509) before we can do this.

[philwebb]

I wonder if we could write our own MetricsCollector implementation so that metrics could be added even if coda metrics wasn't being used. That might be a little tricky since we'd need to do it in spring-boot-actuator and not in spring-boot-autoconfiguration. Perhaps we need a customizer callback for com.rabbitmq.client.ConnectionFactory.

[philwebb]

@acogoluegnes I'm not sure if you have time, but perhaps you could investigate a Spring Boot specific MetricsCollector?

[acogoluegnes]

@philwebb Do you mean something based on Spring Boot's CounterService? That's certainly doable, but we'd need to refactor the implementation that ships with RabbitMQ client to be able to re-use the tricky parts through an abstract class and let sub-classes just increment their metrics. This could be done in 4.0.1. Does that make sense?

[philwebb]

Does that make sense?

Yeah, that would be ideal. I was thinking we'd need to copy/paste a bunch of that code but an abstract base class would be much better.

[acogoluegnes]

I created the issue in the Java Client. How would you like to proceed? Should it be included in the current PR or somewhere else?

[philwebb]

The current PR would be best thanks. You can force push and update to the branch.

[acogoluegnes]

@philwebb Here is the CounterService-based implementation of MetricsCollector. Are you OK with the implementation? If yes, I need to release RabbitMQ Java Client 4.1.0 (the PR uses a snapshot) and ask the Spring AMQP folks to use it in Spring AMQP 2.0.

[acogoluegnes]

@philwebb Any update on this? Please let me know if you're fine with the implementation (especially the ConnectionFactoryCustomizer trick). I'd like to release RabbitMQ Java Client 4.1.0 (which will contain the metrics collector abstract class). No need to merge now, green light is enough. Thanks.

[acogoluegnes]

PR is now based on RabbitMQ Java Client 4.1.0 (through Spring AMQP 2.0), not just a snapshot.

[philwebb]

Duplicates #10887