KEP-4261: Add support for multiple metrics APIs

[JorTurFer]

• One-line PR description:
  Add support for multiple metrics APIs, allowing multiple services exposing metrics on same metric type

• Issue link:
  Support for multiple metrics APIs #4261

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[vsoch]

Thank you for opening this @JorTurFer we need this functionality as well.

[sftim]

Suggested change

It’s another single point of failure.

Kubernetes lets you run replicated services for improved availability. I don't think this is a true drawback.

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/lifecycle stale

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/lifecycle rotten

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/close

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@k8s-triage-robot: Closed this PR.

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/close

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[chicks-net]

/reopen

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[afirth]

/reopen
I don't understand how this gets so little attention. If you run a pre-keda cluster and want to switch, you're going to hit this and end up doing some janky nginx --insecure stuff. It seems like core functionality (HPA) that is now tied to keda implementing everything anyone needs. Let me know if there's anything I can do to help this forward

[k8s-ci-robot]

@afirth: Reopened this PR.

In response to this:

/reopen
I don't understand how this gets so little attention. If you run a pre-keda cluster and want to switch, you're going to hit this and end up doing some janky nginx --insecure stuff. It seems like core functionality (HPA) that is now tied to keda implementing everything anyone needs. Let me know if there's anything I can do to help this forward

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[sftim]

What this improvement needs: willing volunteers that have the capacity. So far, we didn't find some. Personally I'd prefer to see an out-of-tree component that lets you aggregate metric sources, rather than the approach in this KEP. But either way, it's volunteer time and effort that is needed to manage the work around improving Kubernetes. .

[JorTurFer]

We finally decided to go using an external proxy rather than modifying the k8s API. I've created a PoC that verifies to idea to check if it's feasible or not (it is), but I haven't had enough time to finish and publish the project. I hope that it'll be ready during next months

[afirth]

Thanks @JorTurFer, also for your help in the past when I had to deal with this! Do you have a link to the PoC that people could potentially explore or contribute to?
(I came here from kubernetes-sigs/custom-metrics-apiserver#70)

[Jibbscript]

Tyvm for championing this @JorTurFer , I would love to view and possibly contribute to any working PoC you have around the proxy server approach you mentioned above. We are running into this issue while trying to onboard Keptn enterprise wide at a cluster-level when there is an existing metrics apiserver in place for our primary Prometheus monitoring stack.

[LaikaN57]

@JorTurFer +1 for PoC links, if any. Thanks in advance!