⚠️ Remove global metrics registration in init, add registration func

[austince]

This PR removes setting the workqueue global metrics provider in an init method and instead provides a way for consumers of this lib to set it themselves. Otherwise, there is no way to allow consumers to use a different metrics provider.

Also proposed allowing per-queue metrics providers, which would in effect also solve this problem, but the jury's out on it: kubernetes/kubernetes#114242

Closes #2238

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[austince]

cc @alvaroaleman

[alvaroaleman]

As mentioned in the k/k pr, we wont merge this. This breaks the majority use-case (workqueue metrics just work without doing anything) in order to support a minority use-case (set custom provider).

/hold

[austince]

Is this not what you were suggesting here? kubernetes/kubernetes#114242 (comment)

This is marked as a breaking change, and allows consumers to set it. Unsure what the path forward is if it is neither of the options I've proposed.

[alvaroaleman]

No, my suggestion was to change the upstream workqueue to not use a sync.Once so what is set by controller-runtime can be overridden later if desired.

[austince]

Alright, I'll send a PR for that -- seems to paper over the fact that this library is mutating global state and the "metrics just work without doing anything" use case could be addressed somewhere else (like kubebuilder, which sets up a main), but if this gets it in 🤷🏼

I'll leave this open in the meantime if others want to weigh in.

[sbueringer]

I think changing kubebuilder does not really mitigate the situation. I don't have a good overview over the ecosystem but the controllers that I'm aware of don't regularly regenerate their main file with kubebuilder.

[austince]

Okie, I'll close this then -- I've also got a PR for what Alvaro suggested here, if you guys want to drive that approach: kubernetes/kubernetes#116616