Undefined check for apiserver_loadbalancer_domain_name in apiserver_sans

[chadswen]

What type of PR is this?
/kind bug

What this PR does / why we need it:
Defaults apiserver_loadbalancer_domain_name to '' in apiserver_sans, like the other nullable vars in the task, preventing undefined variable related fatal ansible errors.

How to reproduce

When loadbalancer_apiserver_localhost: false and loadbalancer_apiserver.address is not set (e.g. when the nginx-proxy static pod and a load balancer are not desired).

Root Cause

One of the undefined checks for this variable was removed from apiserver_sans in PR 12507 when the set_fact templating was simplified.

However, when loadbalancer_apiserver_localhost: false and loadbalancer_apiserver.address is not set, apiserver_loadbalancer_domain_name defaults to undefined instead of a string as of the cleanup in PR 12872 .

apiserver_loadbalancer_domain_name: "{{ 'localhost' if loadbalancer_apiserver_localhost else (loadbalancer_apiserver.address | d(undef())) }}"

Special notes for your reviewer:
I realize apiserver_loadbalancer_domain_name will be removed eventually by #12897 (which will be a great improvement IMO), but in the meantime this is blocking some of my cluster validation tests that don't provision a load balancer.

Does this PR introduce a user-facing change?:

NONE

[chadswen]

/ok-to-test

[chadswen]

/retest-failed

[VannTen]

Hum, select does not filter undefined? I thought I remembered it did. Did that change in Ansible core 2.18 ? Or I'm just hallucinating stuff 😆 We should also add to one the testcase an explicit loadbalancer_apiserver_localhost: false, to catch that sort of regression.

[VannTen]

/lgtm
/approve
/cherrypick release-2.30

[k8s-infra-cherrypick-robot]

@VannTen: once the present PR merges, I will cherry-pick it on top of release-2.30 in a new PR and assign it to you.

Details

In response to this:

/lgtm
/approve
/cherrypick release-2.30

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chadswen, VannTen

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[k8s-infra-cherrypick-robot]

@VannTen: new pull request created: #13014

Details

In response to this:

/lgtm
/approve
/cherrypick release-2.30

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-sigs/prow repository.