Merge pull request #27060 from xing-yang/dev-1.21

Add doc for volume health monitoring

content/en/docs/concepts/storage/volume-health-monitoring.md

@@ -0,0 +1,32 @@
+---
+reviewers:
+- jsafrane
+- saad-ali
+- msau42
+- xing-yang
+--
+title: Volume Health Monitoring 
+content_type: concept
+---
+
+<!-- overview -->
+
+{{< glossary_tooltip text="CSI" term_id="csi" >}} volume health monitoring allows CSI Drivers to detect abnormal volume conditions from the underlying storage systems and report them as events on {{< glossary_tooltip text="PVCs" term_id="persistent-volume-claim" >}} or {{< glossary_tooltip text="Pods" term_id="pod" >}}.
+
+{{< feature-state for_k8s_version="v1.21" state="alpha" >}}
+
+<!-- body -->
+
+## Volume Health Monitoring
+
+The Volume Health Monitoring feature is part of Kubernetes implementation of Container Storage Interface (CSI). The Volume Health Monitoring feature is implemented in two components: External Health Monitor Controller and Kubelet.
+
+If a CSI Driver supports Volume Health Monitoring feature from the controller side, an event will be reported on the PVC when an abnormal volume condition is detected on a CSI volume.
+
+External Health Monitor Controller will also watch for node failure events. This can be enabled by setting the `enable-node-watcher` flag to true. When a node failure event is detected, an event will be reported on the PVC to indicate that pods using this PVC are on a failed node.
+
+If a CSI Driver supports Volume Health Monitoring feature from the node side, an event will be reported on every Pod using the PVC when an abnormal volume condition is detected on a CSI volume.
+
+Note that you need to enable the `CSIVolumeHealth` feature gate to use this feature from the node side.
+
+See CSI driver [docs](https://kubernetes-csi.github.io/docs/drivers.html) to find out which CSI drivers have implemented this feature.

content/en/docs/reference/command-line-tools-reference/feature-gates.md

@@ -221,6 +221,7 @@ different Kubernetes components.
 | `CSIPersistentVolume` | `false` | Alpha | 1.9 | 1.9 |
 | `CSIPersistentVolume` | `true` | Beta | 1.10 | 1.12 |
 | `CSIPersistentVolume` | `true` | GA | 1.13 | - |
+| `CSIVolumeHealth` | `false` | Alpha | 1.21 | - |
 | `CustomPodDNS` | `false` | Alpha | 1.9 | 1.9 |
 | `CustomPodDNS` | `true` | Beta| 1.10 | 1.13 |
 | `CustomPodDNS` | `true` | GA | 1.14 | - |
@@ -370,7 +371,7 @@ different Kubernetes components.
 | `TokenRequestProjection` | `false` | Alpha | 1.11 | 1.11 |
 | `TokenRequestProjection` | `true` | Beta | 1.12 | 1.19 |
 | `TokenRequestProjection` | `true` | GA | 1.20 | - |
-| `VolumeCapacityPriority` | `false` | Alpha | 1.21 | |
+| `VolumeCapacityPriority` | `false` | Alpha | 1.21 | - |
 | `VolumeSnapshotDataSource` | `false` | Alpha | 1.12 | 1.16 |
 | `VolumeSnapshotDataSource` | `true` | Beta | 1.17 | 1.19 |
 | `VolumeSnapshotDataSource` | `true` | GA | 1.20 | - |
@@ -555,6 +556,7 @@ Each feature gate is designed for enabling/disabling a specific feature:
 - `CSIVolumeFSGroupPolicy`: Allows CSIDrivers to use the `fsGroupPolicy` field.
   This field controls whether volumes created by a CSIDriver support volume ownership
   and permission modifications when these volumes are mounted.
+- `CSIVolumeHealth`: Enable support for CSI volume health monitoring on node.
 - `ConfigurableFSGroupPolicy`: Allows user to configure volume permission change policy
   for fsGroups when mounting a volume in a Pod. See
   [Configure volume permission and ownership change policy for Pods](/docs/tasks/configure-pod-container/security-context/#configure-volume-permission-and-ownership-change-policy-for-pods)