fix(VPA): Do not update webhook CA when registerWebhook is disabled

[vflaux]

What type of PR is this?

/kind bug

What this PR does / why we need it:

This disable the update of CA in the MutatingWebhookConfiguration by the admission controller when the registerWebhook option is not enabled and the CA file changed.

Which issue(s) this PR fixes:

Fixes #8248

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Vertical Pod Autoscaler Admission Controller will not try to update the `vpa-webhook-config` MutatingWebhookConfiguration when `registerWebhook` is disabled.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[omerap12]

/ok-to-test

[omerap12]

Thanks for this

[omerap12]

Correct me if I'm wrong, but in the current implementation, if the flag is off, then mutatingWebhookClient is set to nil, which means the reloadWebhookCA function will always return an error?

[vflaux]

Yes but we don't watch the file when mutatingWebhookClient is nil so we should never call reloadWebhookCA().

[vflaux]

I use mutatingWebhookClient as an indicator of whether registerWebhook is enabled, but introducing a new boolean variable in the struct certReloader might make the code clearer and easier to understand?

[omerap12]

Understood. thanks! adding a comment above line 71 (https://github.com/kubernetes/autoscaler/pull/8249/files#diff-504643e3760ffc997b03797073b201284f6483f8276acd1cf9057c8734e9f5b9R71) will be enough.

[omerap12]

Thanks for this!
/lgtm
/assign @adrianmoisey

[adrianmoisey]

Makes sense, thanks
/approve

@omerap12 should we also backport this change?

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: adrianmoisey, vflaux

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[omerap12]

Makes sense, thanks /approve

@omerap12 should we also backport this change?

Yup!

[adrianmoisey]

This was added in 1.4, so only need to do 1 cherry pick:
/cherry-pick vpa-release-1.4

[k8s-infra-cherrypick-robot]

@adrianmoisey: new pull request created: #8257

In response to this:

This was added in 1.4, so only need to do 1 cherry pick:
/cherry-pick vpa-release-1.4

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