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 (fe6ba6c)

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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 }}

[k8s-ci-robot]

PR needs rebase.

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