Include labelSelector for affinity and topologySpreadConstraints

[pvickery-ParamountCommerce]

Description

The labelSelector is used to track the pods that are used for the topologySpreadConstraints calculation. matchLabelKeys is used to only use the pods in the current version of the deployments replicaset.

I believe the following message isn't true before this PR.

external-dns/charts/external-dns/values.yaml

Lines 155 to 156 in 1ceaf79

	# -- Topology spread constraints for `Pod` [scheduling](https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/). If an explicit label selector is not provided one will be created from the pod selector labels.
	topologySpreadConstraints: []

More details about matchLabelKeys can be found here:

• https://kubernetes.io/docs/concepts/scheduling-eviction/topology-spread-constraints/
• https://kubernetes.io/blog/2023/04/17/fine-grained-pod-topology-spread-features-beta/#kep-3243-respect-pod-topology-spread-after-rolling-upgrades
• https://pauldally.medium.com/the-most-common-reason-your-topologyspreadconstraint-isnt-working-fb9ce25297cd

Checklist

• Unit tests updated
• End user documentation updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: pvickery-ParamountCommerce / name: Patrick Vickery (844bab3)

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[k8s-ci-robot]

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[stevehipwell]

Thanks for the PR @pvickery-ParamountCommerce. The comments in values.yaml were incorrectly copied from a chart where this had been implemented. Did you also see that the same comment was present for affinity? I think we have the following 3 options:

1. Change the comments and don't add default label selectors
2. Implement your pattern for affinity
3. Implement the other pattern

FYI you also need to add a chart CHANGELOG entry under [UNRELEASED].

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[pvickery-ParamountCommerce]

Thanks for the PR @pvickery-ParamountCommerce. The comments in values.yaml were incorrectly copied from a chart where this had been implemented. Did you also see that the same comment was present for affinity? I think we have the following 3 options:

1. Change the comments and don't add default label selectors

2. Implement your pattern for `affinity`

3. Implement the other pattern

FYI you also need to add a chart CHANGELOG entry under [UNRELEASED].

Thanks for the feedback @stevehipwell!
I have implemented the default label selectors in all blocks for podaffinity. I found it to be rather repetitive so let me know if you have any suggestions to simplify it.

I used these values to test affinity when automatically adding the labelSelector, and uncommented the rest to test when the user supplied values should be used.

affinity:
  podAffinity:
    preferredDuringSchedulingIgnoredDuringExecution:
      - weight: 100
        podAffinityTerm:
          topologyKey : "kubernetes.io/hostname"
        # labelSelector:
        #   matchExpressions:
        #     - key: app.kubernetes.io/name
        #       operator: In
        #       values:
        #         - test
    requiredDuringSchedulingIgnoredDuringExecution:
      - topologyKey : "kubernetes.io/hostname"
        # labelSelector:
        #   matchExpressions:
        #     - key: app.kubernetes.io/name
        #       operator: In
        #       values:
        #         - test
  podAntiAffinity:
    preferredDuringSchedulingIgnoredDuringExecution:
      - weight: 100
        podAffinityTerm:
          topologyKey : "kubernetes.io/hostname"
          # labelSelector:
          #   matchExpressions:
          #     - key: app.kubernetes.io/name
          #       operator: In
          #       values:
          #         - test
    requiredDuringSchedulingIgnoredDuringExecution:
      - topologyKey : "kubernetes.io/hostname"
        # labelSelector:
        #   matchExpressions:
        #     - key: app.kubernetes.io/name
        #       operator: In
        #       values:
        #         - test

[stevehipwell]

Could you move the basic structure out into the deployment template, use smaller template functions and make use of with? Something like below (untested).

    {{- with .Values.affinity }}
      affinity:
      {{- with .podAffinity }}
        podAffinity:
        {{- with preferredDuringSchedulingIgnoredDuringExecution }}
        {{- range . }}
        {{- if dig "podAffinityTerm" "labelSelector" nil . }}
          {{- toYaml (list .) | nindent 10 }}
        {{- else }}
          {{ include "external-dns.podAffinityPreferred" . }}
        {{- end }}
        {{- end }}
        {{- end }}
      {{- end }}
      {{- end }}

[pvickery-ParamountCommerce]

Thanks @stevehipwell, that is a good idea! I've updated it with your suggestion and have tested it locally

[stevehipwell]

Could you also look at updating the charts/ci/ci-values.yaml to include coverage for these changes? FYI CI uses a standard Kind cluster .

If this isn't possible we could look at adding a kubconform step to validate the templates.

[pvickery-ParamountCommerce]

Thanks @stevehipwell and sorry for the delay!
I have added my test values to the ci values to setup pod (anti-)affinity and topologySpreadConstraints

[stevehipwell]

/ok-to-test

[stevehipwell]

@pvickery-ParamountCommerce this looks to be failing the lint.

[pvickery-ParamountCommerce]

Ah shoot! I've updated it again to pass the linting checks. preferredDuringSchedulingIgnoredDuringExecution and requiredDuringSchedulingIgnoredDuringExecution values need to be in an array and was just in an object before

[stevehipwell]

Just a couple of comments.

[pvickery-ParamountCommerce]

One more push to fix those findings. I also updatee how the labelSelector is added to remove a useless newline. Thanks again for all the help @stevehipwell!

{{- if dig "labelSelector" nil . }}
-   - {{- toYaml . | nindent 16 }}
+   - {{ toYaml . | indent 16 | trim }}