Add AEP for restoring selector support to VPA

[msudheendra-cflt]

What type of PR is this?

/kind feature
/kind api-change

What this PR does / why we need it:

Created as a follow-up of #8848. This is an AEP for supporting VPA for heterogenous workloads (such as leader/follower)

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[iamzili]

First of all thanks for the AEP! I think it is important to start a discussion around workloads that have heterogeneous resource requirements under the same controller.

we already have one related AEP that tackles Daemonsets: AEP-7942: Vertical Pod Autoscaling for Daemonsets with Heterogeneous Resource Requirements. This proposal could focus on Deployments and Statefulsets, which I believe is its intention

From reading this AEP, it appears to propose solving vertical autoscaling for workloads that use the leader election pattern. The proposed solution assumes that pods under a single controller are labeled by another controller based on which pod is the leader. I think a better approach (or the first use case to address) would be to watch Kubernetes Lease objects directly

At the moment the intent of this AEP seems to be limited to cases where the leader election pattern is used for Deployments/StatefulSets. It would be great to hear what other use cases could lead to heterogeneous resource requirements within the same workload. Off the top of my head, I cannot think of many others as I mostly deal with workloads that are accessed via a Kubernetes Service.

[iamzili]

I think the AEP title should change to reflect that this proposal aims to improve/solve vertical autoscaling for heterogeneous workloads when Deployments and StatefulSets controllers are used. Restoring label selector support is only one part of the solution.

so please make the intention of the AEP in its title more explicit, thanks!

[adrianmoisey]

I worry a little about restoring a field that was once there, I don't know if there are API considerations that need to be made

[adrianmoisey]

What happens if we have 2 VPAs, one with selector of role=primary and another with purpose=web, and a pod were created with both of these labels, that means that both VPAs match that pod.

[omerap12]

How does this solution integrate with controllers?