3041 breaks Helm Rollback

[richardwhiuk]

7eb3523 breaks rollback

Error: cannot patch "core-grafana" with kind PersistentVolumeClaim: PersistentVolumeClaim "core-grafana" is invalid: spec: Forbidden: spec is immutable after creation except resources.requests for bound claims
  core.PersistentVolumeClaimSpec{
      AccessModes:      {"ReadWriteOnce"},
      Selector:         nil,
      Resources:        {Requests: {s"storage": {i: {...}, s: "10Gi", Format: "BinarySI"}}},
-     VolumeName:       "pvc-83d5534d-78b3-492b-8d52-425fcf174ad8",
+     VolumeName:       "",
      StorageClassName: &"managed-premium-zrs",
      VolumeMode:       &"Filesystem",
      ... // 2 identical fields
  }

This is because:

• Helm Release 1, the lookup doesn't find anything, so the spec has ""
• An Upgrade is performed, which has the lookup, so it fills in the volume name.
• A Rollback is performed, the template is not re-evaluated, so the rollback attempts to wipe out the volume name.

Helm errors because this field is immutable.

There's no description in #3041 to explain what kind of upgrade we were doing which hit this issue.

[richardwhiuk]

Workaround is to rollback to Grafana Helm Charts 7.3.8 prior to this change.