Add ExtendedResourceToleration admission controller.

[mindprince]

/kind feature
/sig scheduling
/area hw-accelerators

There's elaborate discussion on this in #55080. In short, we would like to enable cluster operators and/or cloud providers to create dedicated nodes with extended resources (like GPUs, FPGAs etc.) that are reserved for pods requesting such resources. Taints is the kubernetes concept to create dedicated nodes. If the cluster operator or cloud provider wants to create dedicated node pools, they are expected to taint the nodes containing extended resources with the key equal to the name of the resource and effect equal to NoSchedule. If they do that, only pods that have a toleration for such a taint can be scheduled there. To make it easy for the user, this admission controller when enabled, automatically adds a toleration with key example.com/device, operator Exists and effect NoSchedule if an extended resource of name example.com/device is requested.

Release note:

Add ExtendedResourceToleration admission controller. This facilitates creation of dedicated nodes with extended resources. If operators want to create dedicated nodes with extended resources (like GPUs, FPGAs etc.), they are expected to taint the node with extended resource name as the key. This admission controller, if enabled, automatically adds tolerations for such taints to pods requesting extended resources, so users don't have to manually add these tolerations. 

[mindprince]

/assign @vishh @davidopp @bsalamat @jiayingz

[mindprince]

/assign @derekwaynecarr @liggitt

[jiayingz]

/lgtm

[jberkus]

Hey, release team reminder. If this PR is approved, please remember to add the 1.9 milestone and approve it for that milestone by Monday, Nov. 20th to make the Code Slush cutoff. Thanks!

[vishh]

nit: Can this be a function that is something like func podHasWildcardToleration(*api.pod) bool?

[davidopp]

I suspect people don't use wildcard toleration much, and also it might be easier from an understandability perspective (both of the code and someone looking at the pod) if you always add the toleration. So I would suggest to just remove this special case where the wildcard toleration already exists.

[mindprince]

Done.

[vishh]

/lgtm

[k8s-merge-robot]

[MILESTONENOTIFIER] Milestone Pull Request Current

@bsalamat @davidopp @derekwaynecarr @jiayingz @liggitt @mindprince @vishh

Pull Request Labels

• sig/scheduling: Pull Request will be escalated to these SIGs if needed.
• priority/important-soon: Escalate to the pull request owners and SIG owner; move out of milestone after several unsuccessful escalation attempts.
• kind/feature: New functionality.

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[mindprince]

/retest

[davidopp]

/lgtm

[dims]

/assign @liggitt

[caesarxuchao]

A nit. Fix in follow-up PR is fine.

[caesarxuchao]

The result is that such pods can be scheduled to nodes with the "example.com/device" taint, right? Consider adding that in the comment and please also add this plugin to the doc.

[mindprince]

Yes. I will send another PR with the comment fix. And another one to update the public documentation.

[liggitt]

are arbitrary resources allowed? does this give pod authors a way to cause arbitrary taints to be added? I expected a specific prefix/namespace to ensure resource-specific taints were tolerated, not arbitrary taints

[mindprince]

It only adds tolerations for the resource you requested and that resource cannot be in kubernetes.io namespace.

Now you can request an arbitrary string as the resource (and then this will add that arbitrary string as the toleration) but then your pod will not get scheduled because that arbitrary string doesn't exist as a resource. And if the arbitrary string exists as a resource, we do want this admission controller to add that as a toleration.

[liggitt]

Now you can request an arbitrary string as the resource (and then this will add that arbitrary string as the toleration) but then your pod will not get scheduled because that arbitrary string doesn't exist as a resource.

Thinking through this some more:

1. by default, users can already add arbitrary tolerations to their pod specs
2. any cluster using taints/tolerations as a security measure to keep user pods off specific nodes already has to use something like PodTolerationRestriction to whitelist the tolerations a pod is allowed to have
3. that whitelist would give control over allowing custom-resource tolerations while disallowing arbitrary security-related tolerations

So I think this still works as is

[caesarxuchao]

/approve no-issue

[caesarxuchao]

Release note is user facing. Please add a brief description of what the plugin does and who needs it.

[mindprince]

Updated the release note with more details. When the final release notes doc will get generated, I would link this release note to the documentation in kubernetes.io

[caesarxuchao]

@mindprince, regarding @liggitt's question, this line ensures that the resourceName (and the toleration key) has a "kubernetes.io/" or a "pod.alpha.kubernetes.io/opaque-int-resource-" prefix. The "pod.alpha.kubernetes.io/opaque-int-resource-" prefix seems strong enough. But the "kubernetes.io/" seems very generic, will it collide with other taint key name?

[mindprince]

It ensures the opposite. It ensures that the resource name doesn't have kubernetes.io as the prefix.

[caesarxuchao]

Right. I missed the !.

[caesarxuchao]

/hold for @liggitt's question

[caesarxuchao]

/hold

[liggitt]

/hold cancel

[bsalamat]

/lgtm

[k8s-merge-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bsalamat, caesarxuchao, davidopp, jiayingz, mindprince, vishh

Associated issue: 55080

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

Needs approval from an approver in each of these OWNERS Files:

• cmd/kube-apiserver/OWNERS [caesarxuchao]
• plugin/OWNERS [davidopp]

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[k8s-merge-robot]

/test all [submit-queue is verifying that this PR is safe to merge]

[k8s-merge-robot]

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions here.

[dixudx]

Update this admission controller in doc kubernetes/website#6618.