Decouple Startup CPU Boost from VPA modes

[laoj2]

What type of PR is this?

/kind documentation
/kind feature

What this PR does / why we need it:

Changes to AEP-7862:

• Decouple startup boost config from regular VPA, so the API is simplified, in case users want to only use CPU boost without regular VPA updates (we no longer require a new VPA mode + have a way to specify the startup boost config at the VPA/workload level).
• Added more yaml examples

#7862

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[laoj2]

/assign @omerap12
/assign @adrianmoisey

[adrianmoisey]

Could you give a reason why the term Auto was selected here?
I'd assume this field is effectively a boolean, so I'd assume On/Off

[laoj2]

Good point. Wanted to make this similar to regular VPA, but doesn't really make much sense. Changed it to On/Off. Thanks!

[omerap12]

Please look at this: https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md

It says:

"Think twice about bool fields. Many ideas start as boolean but eventually trend towards
a small set of mutually exclusive options. Plan for future expansions by describing the
policy options explicitly as a string type alias (e.g. TerminationMessagePolicy)."

I learned this from @soltysh in this thread

[adrianmoisey]

Good call out, thanks Omer!

[raywainman]

Is the guidance here then to go back to Auto?

[adrianmoisey]

What if we copied ControlledResources?
I wonder if StartupBoost.Resources (or StartupBoostResources?) could be a list that takes memory or cpu in the future, but for now it takes cpu only?

[laoj2]

That's an interesting idea. I'm wondering how we could use it for the use case where we define the "top-level" CPU boost, but want to disable it for an individual container. In the current proposal, it would look like this:

apiVersion: "autoscaling.k8s.io/v1"
kind: VerticalPodAutoscaler
metadata:
  name: example-vpa
spec:
  targetRef:
    apiVersion: "apps/v1"
    kind: Deployment
    name: example
  startupBoost:
    cpu:
      factor: 2.0
  resourcePolicy:
    containerPolicies:
      - containerName: "disable-cpu-boost-for-this-container"
        startupBoost:
          mode: "Off"

So, would we still need an "off"/"none" StartupBoostResources if we want to use this other field, instead? e.g.:

apiVersion: "autoscaling.k8s.io/v1"
kind: VerticalPodAutoscaler
metadata:
  name: example-vpa
spec:
  targetRef:
    apiVersion: "apps/v1"
    kind: Deployment
    name: example
  startupBoost:
    cpu:
      factor: 2.0
  resourcePolicy:
    containerPolicies:
      - containerName: "disable-cpu-boost-for-this-container"
        startupBoost:
          startupBoostResources:
             - "Off"

[laoj2]

Hi folks, in the meantime, I changed this back to Auto. But let me know what you think.

[adrianmoisey]

I'm unsure about "Auto", it seems to be like it's just "Enabled/On", what is automatic about it?

[k8s-ci-robot]

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[raywainman]

Is the guidance here then to go back to Auto?