Add support for topologySpreadConstraints to Helm Chart

[alex-berger]

What this PR does / why we need it:

Adding support for topologySpreadConstraints in Helm chart. This PR is similar in spirit to #949, but it's a bit simpler :-).

Which issue(s) this PR fixes:

• Fixes # Helm chart support for topologySpreadConstraints #948

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[alex-berger]

/assign @stevehipwell

[serathius]

/ok-to-test

[stevehipwell]

@alex-berger out of interest are you planning on running an unknown number of MS pods? If you're running a fixed number of pods I'd have thought an anti-affinity would work better? This is the same question I asked on #949.

[alex-berger]

@alex-berger out of interest are you planning on running an unknown number of MS pods? If you're running a fixed number of pods I'd have thought an anti-affinity would work better? This is the same question I asked on #949.

We use HPA to autoscale instances and TopologySpreadConstraints just works (and scales) better than anti-affinities. There are also some tools which have no or only limited support for anti-affinity. Below some links with more information:

• https://kubernetes.io/docs/concepts/workloads/pods/pod-topology-spread-constraints/#comparison-with-podaffinity-podantiaffinity
• https://github.com/kubernetes/enhancements/tree/master/keps/sig-scheduling/895-pod-topology-spread#motivation
• podAntiAffinity aws/karpenter-provider-aws#942

So, have good reasons to use topologySpreadConstraints instead of PodAntiAffinity :-) and that's the reason why I opened this PR.

[stevehipwell]

/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alex-berger, stevehipwell

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[serathius]

/lgtm