update kubernetes.io/os description as it can also be used in pod labels

[pacoxu]

When I review kubernetes/kubernetes#116892, I find that no document has mentioned it.

	if rejectPodAdmissionBasedOnOSSelector(admitPod, node) {
		return PodAdmitResult{
			Admit:   false,
			Reason:  "PodOSSelectorNodeLabelDoesNotMatch",
			Message: "Failed to admit pod as the `kubernetes.io/os` label doesn't match node label",
		}
	}


...
// rejectPodAdmissionBasedOnOSSelector rejects pod if it's nodeSelector doesn't match
// We expect the kubelet status reconcile which happens every 10sec to update the node labels if there is a mismatch.
func rejectPodAdmissionBasedOnOSSelector(pod *v1.Pod, node *v1.Node) bool {
	labels := node.Labels
	osName, osLabelExists := labels[v1.LabelOSStable]
	if !osLabelExists || osName != runtime.GOOS {
		if len(labels) == 0 {
			labels = make(map[string]string)
		}
		labels[v1.LabelOSStable] = runtime.GOOS
	}
	podLabelSelector, podOSLabelExists := pod.Labels[v1.LabelOSStable]
	if !podOSLabelExists {
		// If the labelselector didn't exist, let's keep the current behavior as is
		return false
	} else if podOSLabelExists && podLabelSelector != labels[v1.LabelOSStable] {
		return true
	}
	return false
}

[pacoxu]

/cc @SergeyKanzhelev @SataQiu

[netlify]

✅ Pull request preview available for checking

Built without sensitive environment variables

Name	Link
🔨 Latest commit	24586e4
🔍 Latest deploy log	https://app.netlify.com/sites/kubernetes-io-main-staging/deploys/64229bec76db100008430c80
😎 Deploy Preview	https://deploy-preview-40332--kubernetes-io-main-staging.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[tengqm]

Suggested change

	When the `kubernetes.io/os` label in Pod labels does not match the node label, the kubelet will not admit the pod. However, this is not taken into account by kube scheduler.
	When the `kubernetes.io/os` label value for a Pod does not match the label value on a Node,
	the kubelet on the node will not admit the Pod. However, this is not taken into account by
	the kube-scheduler.

[sftim]

We might also want to link to https://kubernetes.io/docs/concepts/workloads/pods/#pod-os so that readers are aware that this label is one of two relevant mechanisms.

[pacoxu]

I am unsure if this is the recommended approach.

We might also want to link to https://kubernetes.io/docs/concepts/workloads/pods/#pod-os so that readers are aware that this label is one of two relevant mechanisms.

The Pod OS field seems an alternative way for the pod os label.

[sftim]

I guess this should have a tech review. @pacoxu, who can confirm this revision?

[pacoxu]

I guess this should have a tech review. @pacoxu, who can confirm this revision?

/cc @ravisantoshgudimetla @jsturtevant
who is the owner of IdentifyPodOS and this is part of kubernetes/enhancements#2802. (I opened #40353 as the feature gate was GAed in v1.25 and removed in v1.27.)

Does anything (in-project) set that label on a Pod / pod template?

kubernetes/kubernetes#104613 this was added in v1.23. I cannot find anywhere that is using this label in pod.

[sftim]

/lgtm
as is

Some ideas.

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 2fe280825c1400046b6fc6cbf5739f752a91987b

[sftim]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 835b6bf2d89cd4a1f65d872c03c1660088e53e64

[SataQiu]

/lgtm

[pacoxu]

/assign @sftim

[divya-mohan0209]

LGTM from me!

[sftim]

/approve
based on #40332 (review) as LGTM

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sftim

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• content/en/OWNERS [sftim]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[sftim]

/retitle update kubernetes.io/os description as it can also be used in pod labels