Add extra labels section for per-node options

[Benny-Git]

Ref. #1926 #1574
Add extra labels section for per-node options

This feature was introduced with #1926
I needed something like this, and did not find it in the docs.
After searching some more I found the PR that introduced this, and decided to add it to the docs.

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[BenTheElder]

Thank you!!

rendered: https://deploy-preview-2877--k8s-kind.netlify.app/docs/user/configuration/#extra-labels

given the huge delay I want to just go ahead and proactively merge this, but we should consider mentioning Kubernetes's restrictions on these in a follow-up: https://kubernetes.io/docs/reference/labels-annotations-taints/

Kubernetes reserves all labels and annotations in the kubernetes.io namespace.

which, is actually missing something, it's k8s.io too. will need to go PR the main docs as well https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.16.md#deprecations-and-removals:~:text=removed%20the%20ability%20to%20set%20kubernetes.io%2D%20or%20k8s.io%2Dprefixed%20labels%20via%20%2D%2Dnode%2Dlabels%2C%20other%20than%20the%20specifically%20allowed%20labels/prefixes.%20(%2379305%2C%20%40paivagustavo)

[BenTheElder]

/lgtm
/approve

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[Benny-Git]

which, is actually missing something, it's k8s.io too. will need to go PR the main docs as well

I think the main doc's intention is to document the existing well-known labels and what they should be used for. It does not serve the purpose to inform which prefixes not to use?

The only thing hinting at that limitation is the sentence "Kubernetes reserves all labels and annotations in the kubernetes.io namespace." However I would not interpret the changelog's entry to mean k8s.io is genereally reserved - it looks like this only applies to Node labels?

Edit: Just did a quick test, and deployed a pod with lables k8s.io/benny: test and kubernetes.io/benny: test -- both worked fine.

[BenTheElder]

I think the main doc's intention is to document the existing well-known labels and what they should be used for. It does not serve the purpose to inform which prefixes not to use?

Perhaps, but the first sentence of the page notes that kubernetes.io is reserved.

However I would not interpret the changelog's entry to mean k8s.io is genereally reserved - it looks like this only applies to Node labels?

It's only enforced on node labels, it makes sense there because nodes are owned wholly by kubelet.

The namespaces are still broadly considered reserved for labels, apis, etc. AFAIK.

Unlike kubelet / Node, it makes sense to let third party controllers set labels like app.kubernetes.io/created-by on objects like pod, however it's not intended to invent your own k8s.io labels AFAIK.

There was also a cleanup to move people's CRDs out of k8s.io if they were not approved APIs reviewed by the upstream API review team. kubernetes/enhancements#1111

---

In any case, I'm sure users are going to run into issues with failures trying to set k8s.io and kubernetes.io node labels which will not work since 1.16, we should make sure that's noted somewhere.

/override pull-kind-e2e-kubernetes-1-24

[k8s-ci-robot]

@BenTheElder: Overrode contexts on behalf of BenTheElder: pull-kind-e2e-kubernetes-1-24

In response to this:

I think the main doc's intention is to document the existing well-known labels and what they should be used for. It does not serve the purpose to inform which prefixes not to use?

Perhaps, but the first sentence of the page notes that kubernetes.io is reserved.

However I would not interpret the changelog's entry to mean k8s.io is genereally reserved - it looks like this only applies to Node labels?

It's only enforced on node labels, it makes sense there because nodes are owned wholly by kubelet.

The namespaces are still broadly considered reserved for labels, apis, etc. AFAIK.

Unlike kubelet / Node, it makes sense to let third party controllers set labels like app.kubernetes.io/created-by on objects like pod, however it's not intended to invent your own k8s.io labels AFAIK.

There was also a cleanup to move people's CRDs out of k8s.io if they were not approved APIs reviewed by the upstream API review team. kubernetes/enhancements#1111

---

In any case, I'm sure users are going to run into issues with failures trying to set k8s.io and kubernetes.io node labels which will not work since 1.16, we should make sure that's noted somewhere.

/override pull-kind-e2e-kubernetes-1-24

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