🐛 Fix marshaling of taints, so an empty slice is preserved

[sbueringer]

Signed-off-by: Stefan Büringer [email protected]

What this PR does / why we need it:
This changes the marshalling behavior of taints to make it possible to create control plane machines without taints.

Before:

// * nil => omitted from the marshalled JSON
// * [] => omitted from the marshalled JSON
// * [regular-array] => rendered as usual

After

// * nil => omitted from the marshalled JSON
// * [] => rendered as empty array (`[]`) (<< changed)
// * [regular-array] => rendered as usual

For more details please see the issue (#7149 (comment)).

I think this is a bugfix considering the godoc:

	// Taints specifies the taints the Node API object should be registered with. If this field is unset, i.e. nil, in the `kubeadm init` process
	// it will be defaulted to []v1.Taint{'node-role.kubernetes.io/master=""'}. If you don't want to taint your control-plane node, set this field to an
	// empty slice, i.e. `taints: []` in the YAML file. This field is solely used for Node registration.
	// +optional

Essentially after this PR it's possible to persist and passthrough an empty slice to kubeadm. Before, it was just dropped by our defaulting webhook.

Tested with classy and non-classy cluster. See: https://gist.github.com/sbueringer/5e0ca4417efb22c412155b73bf1bfc32

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #7149

[sbueringer]

/test pull-cluster-api-e2e-full-main

[sbueringer]

/retest
/test pull-cluster-api-e2e-full-main

[sbueringer]

/test pull-cluster-api-e2e-full-main

EDIT: looks like Prow has some issues, let's re-test later

[sbueringer]

@chrischdi I think I tested all relevant variants (see gist linked in the PR description). Maybe you can do some additional smoke test if you have some time. I would really appreciate it!

[sbueringer]

/assign @vincepri @fabriziopandini

[sbueringer]

/hold

Worked a bit with Vince on it, here's a better alternative: #7347

[sbueringer]

Closing for now to avoid confusion between the 2 PRs

/close

[k8s-ci-robot]

@sbueringer: Closed this PR.

In response to this:

Closing for now to avoid confusion between the 2 PRs

/close

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[sbueringer]

/reopen

#7347 (comment)

[k8s-ci-robot]

@sbueringer: Reopened this PR.

In response to this:

/reopen

#7347 (comment)

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[sbueringer]

/test pull-cluster-api-e2e-full-main

[sbueringer]

@fabriziopandini @vincepri
Tests are green. Should be ready for review.

Just doing another run:
/test pull-cluster-api-e2e-full-main

[fabriziopandini]

Thanks for nailing down this problem!
/lgtm

[killianmuldoon]

/lgtm

[sbueringer]

/hold

Just because some folks potentially do some additional validation. Please ignore & still review :)

[vincepri]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vincepri

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[sbueringer]

/hold cancel

(did a few more (successful) local tests)

[k8s-infra-cherrypick-robot]

@sbueringer: once the present PR merges, I will cherry-pick it on top of release 1-2 in a new PR and assign it to you.

In response to this:

/cherry-pick release 1-2

(as discussed in the office hours this week)

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[sbueringer]

/cherry-pick release-1.2

[k8s-infra-cherrypick-robot]

@sbueringer: once the present PR merges, I will cherry-pick it on top of release-1.2 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.2

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[k8s-infra-cherrypick-robot]

@sbueringer: new pull request created: #7366

In response to this:

/cherry-pick release-1.2

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