feat: Allow specification of multiple topology spread constraints

[cfiehe]

This commit adds the possibility to specify multiple topology spread constraints. These constrains are combined using a logical AND operation and control pod distribution across a cluster.

Signed-off-by: Christoph Fiehe fiehe@gmx.de

[CLAassistant]

All committers have signed the CLA.

[sagikazarmark]

This is a bit problematic because it removes the label selectors.

Honestly, I'm not sure how other charts solve this out there.

Would it make sense to merge the list with the label selectors?

[cfiehe]

What we can do - maybe it is not the nicest solution - is to change the code part into:

      {{- with .Values.topologySpreadConstraints }}
      topologySpreadConstraints:
      {{- range . }}
      - {{ . | toYaml | indent 8 | trim }}
        labelSelector:
          matchLabels:
            {{- include "sftpgo.selectorLabels" $ | nindent 12 }}
      {{- end }}
      {{- end }}

Someone can drop the labelSelector in his override and may specify something like:

topologySpreadConstraints:
  - maxSkew: 1
    topologyKey: kubernetes.io/hostname
    whenUnsatisfiable: DoNotSchedule
    matchLabelKeys:
      - pod-template-hash

The result is the following:

      topologySpreadConstraints:
      - matchLabelKeys:
        - pod-template-hash
        maxSkew: 1
        topologyKey: kubernetes.io/hostname
        whenUnsatisfiable: DoNotSchedule
        labelSelector:
          matchLabels:
            app.kubernetes.io/name: sftpgo
            app.kubernetes.io/instance: sftpgo

It is the same approach that is used here.

What do you think?

[cfiehe]

Improved version with merge:

      {{- with .Values.topologySpreadConstraints }}
      topologySpreadConstraints:
      {{- range $constraint := . }}
      {{- if not $constraint.labelSelector }}
      {{- $selectorLabels := fromYaml (include "sftpgo.selectorLabels" $)}}
      {{- $constraint = merge $constraint (dict "labelSelector" (dict "matchLabels" $selectorLabels)) }}
      {{- end }}
      - {{ $constraint | toYaml | indent 8 | trim }}
      {{- end }}
      {{- end }}

This version adds the default, when no labelSelector has been specified - which should be the normal case.

[cfiehe]

@sagikazarmark @drakkan
Are there any chances to get this enhancement merged?