Add documentation for probe-level grace period overrides

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

@@ -146,6 +146,7 @@ different Kubernetes components.
 | `PodAffinityNamespaceSelector` | `false` | Alpha | 1.21 | |
 | `PodOverhead` | `false` | Alpha | 1.16 | 1.17 |
 | `PodOverhead` | `true` | Beta | 1.18 |  |
+| `ProbeTerminationGracePeriod` | `false` | Alpha | 1.21 | |
 | `ProcMountType` | `false` | Alpha | 1.12 | |
 | `QOSReserved` | `false` | Alpha | 1.11 | |
 | `RemainingItemCount` | `false` | Alpha | 1.15 | |
@@ -697,6 +698,9 @@ Each feature gate is designed for enabling/disabling a specific feature:
 - `PodShareProcessNamespace`: Enable the setting of `shareProcessNamespace` in a Pod for sharing
   a single process namespace between containers running in a pod.  More details can be found in
   [Share Process Namespace between Containers in a Pod](/docs/tasks/configure-pod-container/share-process-namespace/).
+- `ProbeTerminationGracePeriod`: Enable [setting probe-level
+  `terminationGracePeriodSeconds`](/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/#probe-level-terminationGracePeriodSeconds)
+   on pods.  See the [enhancement proposal](https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/2238-liveness-probe-grace-period) for more details.
 - `ProcMountType`: Enables control over the type proc mounts for containers
   by setting the `procMount` field of a SecurityContext.
 - `QOSReserved`: Allows resource reservations at the QoS level preventing pods

content/en/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes.md

@@ -427,7 +427,48 @@ For a TCP probe, the kubelet makes the probe connection at the node, not in the
 means that you can not use a service name in the `host` parameter since the kubelet is unable
 to resolve it.
 
+### Probe-level `terminationGracePeriodSeconds`
 
+{{< feature-state for_k8s_version="v1.21" state="alpha" >}}
+
+Prior to release 1.21, the pod-level `terminationGracePeriodSeconds` was used
+for terminating a container that failed its liveness or startup probe. This
+coupling was unintended and may have resulted in failed containers taking an
+unusually long time to restart when a pod-level `terminationGracePeriodSeconds`
+was set.
+
+In 1.21, when the feature flag `ProbeTerminationGracePeriod` is enabled, users
+can specify a probe-level `terminationGracePeriodSeconds` as part of the probe
+specification. When the feature flag is enabled, and both a pod- and
+probe-level `terminationGracePeriodSeconds` are set, the kubelet will use the
+probe-level value.
+
+For example,
+
+```yaml
+spec:
+  terminationGracePeriodSeconds: 3600  # pod-level
+  containers:
+  - name: test
+    image: ...
+
+    ports:
+    - name: liveness-port
+      containerPort: 8080
+      hostPort: 8080
+
+    livenessProbe:
+      httpGet:
+        path: /healthz
+        port: liveness-port
+      failureThreshold: 1
+      periodSeconds: 60
+      # Override pod-level terminationGracePeriodSeconds #
+      terminationGracePeriodSeconds: 60
+```
+
+Probe-level `terminationGracePeriodSeconds` cannot be set for readiness probes.
+It will be rejected by the API server.
 
 ## {{% heading "whatsnext" %}}