proposal(sts): placement of volumes from a single statefulset

ProblemStatement: A statefulset can be deployed with multiple replicas. In addition, each replica can be configured to use one or more persistent volumes. While due care can be taken to spread the statefulset application replicas across zones or nodes, similar strategy needs to be followed for these replicas' backing volume(s). It will be good to ensure these volumes are spread out & are never placed on a single node or single zone.

Possible Solution: Specific statefulsets can be watched (via k8s controllers) & their corresponding volume claims can be tracked. The volume claims can further be filtered based on the storage class. Once required details are achieved, these information can be saved in a new custom resource. This should ensure storage provisioners to run through their volume placement decisions.

# This custom resource will select statefulset whose volume info need
# to tracked & saved
kind: StatefulsetVolumePolicy
spec:
   # select a StatefulSet based on following criterias
   select:
     matchLabels:
     matchAnnotations:
     matchFields:
   placement:
     # spread will spread the volumes across zones or across hosts or
     # will get placed based on corresponding application pods
     spread: # Zone, Host, Pod
     # topology can be used to further determine which zones, hosts, etc
     # these volumes should get placed
     topology:
       hosts:
       - host 2
       - host 3

kind: VolumeGroup
spec:
   refer:
      kind: StatefulSet
      apiVersion: apps/v1
      name: my-sts
      namespace: my-ns
  volumes:
  - pvcName:
    podName:
    podNodeName:

Start by reviewing the repository's existing Kubernetes controller and metacontroller patterns, then compare them with StatefulSet, PVC, pod, node, and topology behavior. The proposed StatefulsetVolumePolicy and VolumeGroup resources need a concrete scope, reconciliation behavior, and acceptance criteria before implementation can be considered done.