Merge pull request #4713 from carlory/kep-3751

update VolumeAttributesClass Deletion Protection

keps/sig-storage/3751-volume-attributes-class/README.md

@@ -437,46 +437,38 @@ Operation metrics from [csiOperationsLatencyMetric](https://github.com/kubernete
 
 #### VolumeAttributesClass Deletion Protection
 
-While a VolumeAttributesClass is referenced by any PVC, we will prevent the object from being deleted by adding a finalizer([reference](https://github.com/kubernetes/kubernetes/blob/master/plugin/pkg/admission/storage/storageobjectinuseprotection/admission.go)). 
+While a VolumeAttributesClass is referenced by any PVC, we will prevent the object from being deleted by adding a finalizer `kubernetes.io/vac-protection`. It's a best effort to prevent users from making mistakes. It may not be accurate in all cases.
 
-The **vac_finalizer_controller** sets/removes the finalizer on all VolumeAttributesClasses. This prevents users from deleting a VolumeAttributesClass that's used by a PVC. The vac_finalizer_controller will maintain a cache of a map of VolumeAttributesClass to the list of PVCs that are using the VolumeAttributesClass.
+The **vac_finalizer_controller** sets/removes the finalizer on all VolumeAttributesClasses. It has PVC/PV informers with a custom indexer which is used to list all PVCs/PVs for a given VolumeAttributesClass name. 
 
-There are a few conditions that will trigger add/remove pvc finalizers in the VolumeAttributesClass:
+There are a few conditions that will trigger add/remove the finalizer in the VolumeAttributesClass:
 
 1. PVC created with a VolumeAttributesClass
     The **vac_finalizer_controller**:
-    * If the VolumeAttributesClassName is nil or empty, the VolumeAttributesClass will not be added to the vac_finalizer_controller cache
-    * Check if the VolumeAttributesClass exists. If not, the VolumeAttributesClass will not be added to the vac_finalizer_controller cache
+    * If the VolumeAttributesClassName is nil or empty, do nothing.
+    * Check if the VolumeAttributesClass exists. If not, do nothing.
     * Check if this VolumeAttributesClass already has a protection finalizer
     * Add the finalizer to the VolumeAttributesClass if there is none 
-2. PVC created with a VolumeAttributesClass being deleted
-    The **vac_finalizer_controller**:
-    * Check VolumeAttributesClass is being deleted and PVC creation failed
-3. PVC updated to a different VolumeAttributesClass
-    * The **vac_finalizer_controller** will remove finalizer in the VolumeAttributesClass only if after listing all the PVCs/PVs and confirm that this PVC/PV is the last one that is consuming the VolumeAttributesClass in the vac_finalizer_controller cache
+2. PVC updated to a different VolumeAttributesClass
+    * The **vac_finalizer_controller** will remove finalizer in the VolumeAttributesClass only if after listing all the PVCs/PVs from informers via a custom indexer and confirm that this PVC/PV is the last one that is consuming the VolumeAttributesClass in the vac_finalizer_controller cache
     * Check if the new VolumeAttributesClass already has a protection finalizer
-    * Add the finalizer to the new VolumeAttributesClass if there is none 
-4. PVC updated to a different VolumeAttributesClass that is being deleted
-    The **vac_finalizer_controller**:
-    * Check VolumeAttributesClass is being deleted and PVC update failed
-5. PVC has a VolumeAttributesClass and this PVC is deleted
-    * The **vac_finalizer_controller** will remove finalizer in the VolumeAttributesClass only if after listing all the PVCs/PVs and confirm that this PVC/PV is the last one that is consuming the VolumeAttributesClass in the informer(a cache of VolumeAttributesClass) **only**
-6. Delete a VolumeAttributesClass while there is **kubernetes.io/vac-protection** finalizer associated with this VolumeAttributesClass
-    * Deletion will not return an error but it will add a deletionTimestamp and wait for the finalizer being removed, then remove the VolumeAttributesClass
-7. Delete a VolumeAttributesClass without any finalizers
-    * Deletion succeed
+    * Add the finalizer to the new VolumeAttributesClass if there is nones
+3. PVC has a VolumeAttributesClass and this PVC is deleted
+    * The **vac_finalizer_controller** will remove finalizer in the VolumeAttributesClass only if after listing all the PVCs/PVs from informers via a custom indexer and confirm that this PVC/PV is the last one that is consuming the VolumeAttributesClass in the informer(a cache of VolumeAttributesClass) **only**
+4. Delete a VolumeAttributesClass while there is **kubernetes.io/vac-protection** finalizer associated with this VolumeAttributesClass
+    * Remove the finalizer only if there is no PVC/PV using this VolumeAttributesClass anymore. The check logic is the same as above.
 
-For unbound PVs referencing a VAC:
+For PVs referencing a VAC:
 
 1. Unbound PV created with a VolumeAttributesClass
     The **vac_finalizer_controller**:
-    * If the VolumeAttributesClassName is nil or empty, the VolumeAttributesClass will not be added to the vac_finalizer_controller cache
+    * If the VolumeAttributesClassName is nil or empty, do nothing
     * Check if this VolumeAttributesClass already has a protection finalizer
     * Add the finalizer to the VolumeAttributesClass if there is none
 2. PV has a VolumeAttributesClass and this PV is deleted
-    * The **vac_finalizer_controller** will remove finalizer in the VolumeAttributesClass only if after listing all the PVCs/PVs and confirm that this PVC/PV is the last one that is consuming the VolumeAttributesClass in the informer(a cache of VolumeAttributesClass) **only**
+    * The **vac_finalizer_controller** will remove finalizer in the VolumeAttributesClass only if after listing all the PVCs/PVs from informers via a custom indexer and confirm that this PVC/PV is the last one that is consuming the VolumeAttributesClass in the informer(a cache of VolumeAttributesClass) **only**
 
-Only the **vac_finalizer_controller** will remove finalizers on VolumeAttributesClass. If the **vac_finalizer_controller** fails at the step of removing finalizer even there is no PVC/PV using the VolumeAttributesClass anymore, the **vac_finalizer_controller** should retry the deletion as a separate go routine.
+Only the **vac_finalizer_controller** will remove finalizers on VolumeAttributesClass. If the **vac_finalizer_controller** fails at the step of removing finalizer even there is no PVC/PV using the VolumeAttributesClass anymore, the **vac_finalizer_controller** should retry it in next reconcile loop.
 
 The vac_finalizer_controller will use only informers and therefore it may remove the finalizer too early. One scenario is:
 
@@ -888,7 +880,7 @@ For each of them, fill in the following information by copying the below templat
       levels that could help debug the issue?
       Not required until feature graduated to beta.
     - Testing: Are there any tests for failure mode? If not, describe why.
--->
+    -->
 
 ###### What steps should be taken if SLOs are not being met to determine the problem?