kubeadm: Let the --node-name flag flow down to --hostname-override for the kubelet

[liztio]

What this PR does / why we need it:

Kubeadm-initialised kubelet uses provided hostname if present

If --node-name is passed in to kubeadm init, --hostname-override will be
passed to kubelet. This prevents timeout errors for kubeadm init.

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 kubernetes/kubeadm#846

Special notes for your reviewer:
Depends on #64624 to work fully, but can safely merged before hand.

Release note:

[action required] The `--node-name` flag for kubeadm now dictates the Node API object name the
kubelet uses for registration, in all cases but where you might use an in-tree cloud provider.
If you're not using an in-tree cloud provider, `--node-name` will set the Node API object name.
If you're using an in-tree cloud provider, you MUST make `--node-name` match the name the
in-tree cloud provider decides to use.

[liztio]

/cc @kubernetes/sig-cluster-lifecycle-pr-reviews

[liztio]

/test pull-kubernetes-e2e-gce

[luxas]

Code-wise I'm happy with this, but we have to clearly document the change in behavior we have here.
Earlier --node-name let you change the SAN of the cert so it matches the name the kubelet decides to have by using autodetection.
Now we basically force the kubelet to have the node name you give to kubeadm.

Further, it seems --hostname-override has no effect at all when using at least in-tree cloud providers: #64661

/lgtm
/assign @timothysc
for the second approval

[timothysc]

generally I approve, but I have a question about usage and how this overlaps with your other patch, b/c people can muck it up pretty easily.

[timothysc]

given that the most common thing folks do is use fully qualified domain names I'm almost wondering if we should force tolower on the names similar to your other patch.

[liztio]

I just tested this, and it appears this already happens automatically:

ubuntu@ip-172-31-84-104:~$ sudo /tmp/kubeadm init -v 1 --pod-network-cidr=192.168.0.0/16 --node-name ALLCAPS.horse

ubuntu@ip-172-31-84-104:~$ kubectl get nodes
NAME            STATUS    ROLES     AGE       VERSION
allcaps.horse   Ready     master    44s       v1.11.0-beta.0

I don't particularly know how, but I think this is a nonissue either way.

[luxas]

The nodeutil.GetHostname() func lowercases automatically:

// GetHostname returns OS's hostname if 'hostnameOverride' is empty; otherwise, return 'hostnameOverride'.
func GetHostname(hostnameOverride string) string {
	hostname := hostnameOverride
	if hostname == "" {
		nodename, err := os.Hostname()
		if err != nil {
			glog.Fatalf("Couldn't determine hostname: %v", err)
		}
		hostname = nodename
	}
	return strings.ToLower(strings.TrimSpace(hostname))
}

[luxas]

/milestone v1.11
/status approved-for-milestone
/kind feature
/priority critical-urgent

[fabriziopandini]

thanks @liztio!
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini, liztio, luxas

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[k8s-github-robot]

[MILESTONENOTIFIER] Milestone Pull Request: Up-to-date for process

@fabriziopandini @liztio @luxas @timothysc

Pull Request Labels

• sig/cluster-lifecycle: Pull Request will be escalated to these SIGs if needed.
• priority/critical-urgent: Never automatically move pull request out of a release milestone; continually escalate to contributor and SIG through all available channels.
• kind/feature: New functionality.

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