fix implementation and risks section

kubernetes · Dec 22, 2018 · d9ea0b2 · d9ea0b2
1 parent 623cceb
commit d9ea0b2
Showing 1 changed file with 8 additions and 6 deletions.
diff --git a/keps/sig-apps/0034-20181220-statefulset-volume-expansion.md b/keps/sig-apps/0034-20181220-statefulset-volume-expansion.md
@@ -13,7 +13,7 @@ approvers:
   - TBD
 editor: TBD
 creation-date: 2018-12-20
-last-updated: 2018-12-20
+last-updated: 2018-12-22
 status: provisional
 see-also:
   - n/a
@@ -65,17 +65,19 @@ Allow for increases to storage requests in the `volumeClaimTemplates` component
 
 The apiserver will allow for increases to storage requests in the `volumeClaimTemplates` component of a StatefulSet.
 
-During the StatefulSet update process, the StatefulSet controller will detect an update to a `volumeClaimTemplate` by comparing the updated and current revision of the StatefulSet.
+During the StatefulSet update process, the StatefulSet controller will detect an update to a `volumeClaimTemplate` by comparing the updated and current revision of the StatefulSet. This requires the `VolumeClaimTemplates` component of the StatefulSet to be recorded in the StatefulSet's `ControllerRevision` object.
 
 While updating a pod, the StatefulSet controller will update a referenced persistent volume claim object if its storage request in the associated `volumeClaimTemplate` has been increased.
 
-The pod will be restarted after the `FileSystemResizePending` condition is True on all updated persistent volume claims it references.
+The Statefulset controller will delete and recreate the pod after the `FileSystemResizePending` condition is True on all updated persistent volume claims it references. However, if the `ExpandInUsePersistentVolumes` feature is enabled, then deleting the pod is unnecessary to complete file system expansion on updated persistent volumes.
 
-### Risks and Mitigations
+The functionality provided by this enhancement will be gated by the `StatefulSetVolumeExpansion` feature gate.
 
-Under the `ExpandPersistentVolumes` feature, pods referencing a volume must be restarted for file system expansion to occur after the `FileSystemResizePending` condition is True on the persistent volume claim. If the StatefulSet is configured with the `RollingUpdate` update strategy, then the StatefulSet controller would need to wait for the `FileSystemResizePending` condition to be satisfied on each persistent volume claim referenced by the pod it is updating before restarting the pod. This could noticeably increase the update time of a StatefulSet with many replicas. 
+### Risks and Mitigations+
 
-A potential mitigation would be the eventual adoption of the `ExpandInUsePersistentVolumes` alpha feature in Kubernetes v1.11 which enables file system expansion on volumes being used by a pod.  
+If the `ExpandInUsePersistentVolumes` alpha feature in Kubernetes v1.11 is not enabled when expanding a volume, then pods referencing the volume must be deleted and recreated for file system expansion to occur after the `FileSystemResizePending` condition is True on the persistent volume claim. If the StatefulSet is configured with the `RollingUpdate` update strategy, then the StatefulSet controller would need to wait for the `FileSystemResizePending` condition to be satisfied on each persistent volume claim referenced by the pod it is updating before restarting the pod. This could noticeably increase the update time of a StatefulSet with many replicas. 
+
+A potential mitigation would be the eventual adoption of the `ExpandInUsePersistentVolumes` feature, which enables file system expansion on in-use volumes thus, making it unecessary to delete and recreate any refrencing pods during volume expansion.
 
 ## Graduation Criteria