fix(kubernetes/preinstall): skip when dir is empty

[shaleenbathla]

useful especially for setting manifests dir as empty

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change

/kind bug

/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:
allows setting kube_manifests dir as empty and we should rightfully skip when other dir are empty as well

Which issue(s) this PR fixes:

Fixes #13281

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

bugfix(preinstall): skip kube_manifest_dir dir creation when empty

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[yankay]

/ok-to-test

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: neilamoore, shaleenbathla
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[guoard]

The change itself looks good, but it only fixes the dir creation. A few more things are needed before kube_manifest_dir: "" really works:

• kubelet-config.v1beta1.yaml.j2 still renders staticPodPath: {{ kube_manifest_dir }} unconditionally. Empty var gives staticPodPath: (null), which kubelet happens to accept, but it should be wrapped in {% if kube_manifest_dir %} to make the intent explicit.
• With the default localhost apiserver LB, workers get an nginx-proxy static pod written to {{ kube_manifest_dir }}/nginx-proxy.yml. With the var empty that becomes /nginx-proxy.yml and the pod never runs, so workers lose the apiserver. This setup only works with an external loadbalancer_apiserver.
• Should also be documented that this must be set in worker group_vars only, control plane nodes still need the manifests dir for kubeadm.

Nit: release note says kube_manifests_dir, the variable is kube_manifest_dir.

[shaleenbathla]

The change itself looks good, but it only fixes the dir creation. A few more things are needed before kube_manifest_dir: "" really works:

• kubelet-config.v1beta1.yaml.j2 still renders staticPodPath: {{ kube_manifest_dir }} unconditionally. Empty var gives staticPodPath: (null), which kubelet happens to accept, but it should be wrapped in {% if kube_manifest_dir %} to make the intent explicit.
• With the default localhost apiserver LB, workers get an nginx-proxy static pod written to {{ kube_manifest_dir }}/nginx-proxy.yml. With the var empty that becomes /nginx-proxy.yml and the pod never runs, so workers lose the apiserver. This setup only works with an external loadbalancer_apiserver.
• Should also be documented that this must be set in worker group_vars only, control plane nodes still need the manifests dir for kubeadm.

Nit: release note says kube_manifests_dir, the variable is kube_manifest_dir.

thanks for the review @guoard. updated release note, added explicit conditional, added docs
please re-review the latest changes

[guoard]

Thank you for your contribution.
/lgtm
Not sure about the release note though, would like a second opinion on that.

[VannTen]

• With the default localhost apiserver LB, workers get an nginx-proxy static pod written to {{ kube_manifest_dir }}/nginx-proxy.yml. With the var empty that becomes /nginx-proxy.yml and the pod never runs, so workers lose the apiserver. This setup only works with an external loadbalancer_apiserver.
• Should also be documented that this must be set in worker group_vars only, control plane nodes still need the manifests dir for kubeadm

The first can be asserted against, and IMO should be as this can do some damage on a cluster. (validate_inventory should be good enough for that).
I don't remember if assert are per-host , but if yes then the second is trivial to assert as well, so we should probably do it as well.
Except for that this looks good.
The release note should probably be something like "allow empty kube_manifest_dir on workers to disable static pods" or something like that.

Also, nit, but IMO item != "" is clearer on the intent than using length > 0.

[guoard]

but IMO item != "" is clearer on the intent than using length > 0

what about when item is a list and not string?

[VannTen]

> but IMO item != "" is clearer on the intent than using length > 0 what about when item is a list and not string?

Well those are paths right ? A list would not make sense here. If you mean in general, well, I'd just just == [] for lists. (but I tend to filter the list before the loop with select anyway ^^)

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-- Max Gautier