Add namespace label selector

[RomanenkoDenys]

Added namespace label selector for filtering pods in the DefaultEvictor plugin.
This is useful when descheduler uses only, for example, in the stage or dev namespaces.

[k8s-ci-robot]

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @RomanenkoDenys. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[a7i]

/ok-to-test

would you please squash your commits?

[a7i]

@RomanenkoDenys great feature! would you be open to adding an e2e test for this?

[ingvagabund]

E.g. LowNodeUtilization plugin will not like it:

descheduler/pkg/framework/plugins/nodeutilization/lownodeutilization.go

Line 54 in a3146a1

WithFilter(handle.Evictor().Filter).

. The plugin needs to evaluate all the pods so it can properly compute the resource utilization. There's EvictableNamespaces complement field which matches the namespaces right before eviction. Putting the namespace filtering here would break the plugin's functionality. The same for HighNodeUtilization or any plugin that balances pods on the cluster scope.

This needs to go under PreEvictionFilter extension point. In the case of having each plugin to decide whether it wants to perform namespace filtering before balancing/descheduling pods the filtering needs to be added in each plugin's New function. Or in case namespaces are iterated explicitly in the corresponding methods (if it can not be done as part of pod filtering). E.g.

descheduler/pkg/framework/plugins/removepodsviolatingtopologyspreadconstraint/topologyspreadconstraint.go

Lines 124 to 128 in a3146a1

	var includedNamespaces, excludedNamespaces sets.Set[string]
	if d.args.Namespaces != nil {
	includedNamespaces = sets.New(d.args.Namespaces.Include...)
	excludedNamespaces = sets.New(d.args.Namespaces.Exclude...)
	}

.

[RomanenkoDenys]

Hi, I think you are right. But i have one question. In front of my code there is a constraint for podLabelSelector. And this selector theoretically does not allow to compute all pods, because we can label pods and remove them from the computation using pod label selector.

Icluding/excluding namespaces by name list is not acceptable for us, because in this case we cannot work with dynamically created namespaces (e.g. for dev environments). Using a label selector is our preferred method.

[ingvagabund]

Is this part of #1499? Or, is your PR a parallel/independent effort?

[ingvagabund]

But i have one question.

Which question is it? I see only statements.

[RomanenkoDenys]

Yes, it's a part of #1499. The question is, if you can select pods using a label selector, how will the computational resources of all pods work? And why selecting pods by namespace label selector differs from pod label selector in that case ?

[RomanenkoDenys]

ok, thanks, i'll move the label selector code to the PreEvictionFilter. Now i understand your logic. It is a pity that this is not also explained in detail in the documentation ).

[RomanenkoDenys]

Code moved to the preEvictionFilter. Please check it again.

[RomanenkoDenys]

@ingvagabund hello. Can you help me ? Now namespaces list by label selector calculated for every pod which is passed to the PreEvictionFilter. I think we can calculate namespaces name list and pass it to the PreEvictionFilter to reduce cpu usage (i think we can calculate it on every Descheduler Loop). Please advise where this can be done.

[ingvagabund]

You could create a new namespace indexer storing namespaces based on a label selector. Which will give you all the namespaces at any given point for free.

[RomanenkoDenys]

Hello, i rebased to current main and add indexer. Can you please check implementation ? If all ok, i'll add tests.

[k8s-ci-robot]

@RomanenkoDenys: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-descheduler-verify-master	1b6910e	link	true	/test pull-descheduler-verify-master

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[RomanenkoDenys]

/ok-to-test

would you please squash your commits?

Yes, when i stabilize code, i will squash commits. Thank you !

[clementnuss]

@RomanenkoDenys do you need help ? we will soon need that feature, I'm happy to take this PR to completion and fix the open points.
PS, available on K8s slack to further discuss.

[RomanenkoDenys]

@RomanenkoDenys do you need help ? we will soon need that feature, I'm happy to take this PR to completion and fix the open points. PS, available on K8s slack to further discuss.

Hello, no, thanks. Today i pushed new implementation as we discussed with @ingvagabundand and rebase to current master branch. I need one more day to do some tests. Can you check PR after that ? If implementation is ok i'll write tests for it.

[RomanenkoDenys]

@clementnuss can you please check implementation ?

[clementnuss]

@clementnuss can you please check implementation ?

I could but I'm not a contributor of the repo, sorry if my comment implied that. I think it's best if the assigned people have a chance to look at it, I'd have to first get familiar with the codebase. sorry!