From https://github.com/openshift/hypershift/issues/369

We anticipate multi-zonal spread of control plane components to be a common requirement (e.g. https://github.com/openshift/hypershift/issues/227).

One approach that we think may satisfy the majority use case is to define multi-zonal in terms of anti-affinity rules based on the `topology.kubernetes.io/zone` topology key for pod anti-affinity. This proposal is to set default anti-affinity rules for control plane components deployments like:

podAntiAffinity:
  requiredDuringSchedulingIgnoredDuringExecution:
  - labelSelector:
      matchExpressions:
      - key: app
        operator: In
        values: [...]
    topologyKey: "topology.kubernetes.io/zone"

These defaults would apply regardless of HA mode on the hostedcluster and would ensure that basic multi-zone spreading is implemented by default. If this satisfies the known use cases, we don't need any generic configuration API for anti-affinity at this time.

TODO: Define the exhaustive list of control plane components which to which these defaults will be applied.