feat(recommender): add enforce cpu memory ratio

[Jrmy2402]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds --enforce-cpu-memory-ratio flag to the VPA recommender, allowing users to enforce a fixed memory-per-CPU ratio (expressed as bytes per millicores) across all resource recommendations.
This ensures that CPU and memory recommendations remain balanced according to a user-defined ratio, automatically adjusting one resource when the other changes.

Special notes for your reviewer:

Does this PR introduce a user-facing change?

The ratio is applied to Target, LowerBound, UpperBound, and UncappedTarget recommendations.
The value of --enforce-cpu-memory-ratio should be specified in bytes per millicores (e.g., 4294967.296 for 1 CPU → 4 GiB).

feat(recommender): add enforce cpu memory ratio

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Jrmy2402 / name: Jérémy S (0a85516, c967445)

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[omerap12]

Thanks for this!
I didn't review it yet but I thought new flags should be behind a feature flag?
@adrianmoisey

[jackfrancis]

/release-note feat(recommender): add enforce cpu memory ratio

[adrianmoisey]

/ok-to-test

[adrianmoisey]

I'm wondering if this change makes sense as a flag. It seems that moving these sorts of configurable option to the VPA API would seem to be more desirable, as a user may want to enable this on a subset of workloads controlled by the VPA

[omerap12]

desirable, as a user may want to enable this on a subset of workloads controlled by the VPA

Yeah totally agree here.

[Jrmy2402]

Ok, thanks for the review. I'll rework the MR to handle this via the VPA API.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Jrmy2402
Once this PR has been reviewed and has the lgtm label, please assign raywainman for approval. For more information see the Code Review Process.

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[Jrmy2402]

Update: switched from the global --enforce-cpu-memory-ratio flag to the new MemoryPerCPU field in the VPA API (configurable per container in PodResourcePolicy).

[omerap12]

This should be behind an alpha feature flag with default off

[adrianmoisey]

Does this type of change need an AEP? I assume so, since it's an API change. Sorry for the extra scope.

[Jrmy2402]

Ok I will add an alpha feature flag with default off next week.
For the AEP, I need to check what I need to do, I have never done it before

[omerap12]

Ok I will add an alpha feature flag with default off next week.

For the AEP, I need to check what I need to do, I have never done it before

We added a lot of AEPs lately, you can look at some of them to get the hang of it. It's pretty straightforward.

[adrianmoisey]

For the AEP, I need to check what I need to do, I have never done it before

It's similar to the KEP process for Kubernetes, but it's much more light weight. We are trying to ensure a high standard and also keep the standard similar to Kubernetes (ie: API review, feature gates, etc), but they aren't that hard to do, and as Omer suggested, take a look at the most recent ones.

They live in https://github.com/kubernetes/autoscaler/tree/master/vertical-pod-autoscaler/enhancements