Merge pull request #24692 from SergeyKanzhelev/ExecProbeTimeout

ExecProbeTimeout feature gate introduction

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

@@ -227,6 +227,7 @@ different Kubernetes components.
 | `EvenPodsSpread` | `false` | Alpha | 1.16 | 1.17 |
 | `EvenPodsSpread` | `true` | Beta | 1.18 | 1.18 |
 | `EvenPodsSpread` | `true` | GA | 1.19 | - |
+| `ExecProbeTimeout` | `true` | GA | 1.20 | - |
 | `GCERegionalPersistentDisk` | `true` | Beta | 1.10 | 1.12 |
 | `GCERegionalPersistentDisk` | `true` | GA | 1.13 | - |
 | `HugePages` | `false` | Alpha | 1.8 | 1.9 |
@@ -453,6 +454,7 @@ Each feature gate is designed for enabling/disabling a specific feature:
 - `EphemeralContainers`: Enable the ability to add {{< glossary_tooltip text="ephemeral containers"
   term_id="ephemeral-container" >}} to running pods.
 - `EvenPodsSpread`: Enable pods to be scheduled evenly across topology domains. See [Pod Topology Spread Constraints](/docs/concepts/workloads/pods/pod-topology-spread-constraints/).
+- `ExecProbeTimeout`: Ensure kubelet respects exec probe timeouts. This feature gate exists in case any of your existing workloads depend on a now-corrected fault where Kubernetes ignored exec probe timeouts. See [readiness probes](/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/#configure-probes).
 - `ExpandInUsePersistentVolumes`: Enable expanding in-use PVCs. See [Resizing an in-use PersistentVolumeClaim](/docs/concepts/storage/persistent-volumes/#resizing-an-in-use-persistentvolumeclaim).
 - `ExpandPersistentVolumes`: Enable the expanding of persistent volumes. See [Expanding Persistent Volumes Claims](/docs/concepts/storage/persistent-volumes/#expanding-persistent-volumes-claims).
 - `ExperimentalCriticalPodAnnotation`: Enable annotating specific pods as *critical* so that their [scheduling is guaranteed](/docs/tasks/administer-cluster/guaranteed-scheduling-critical-addon-pods/).

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

@@ -336,6 +336,28 @@ liveness. Minimum value is 1.
 try `failureThreshold` times before giving up. Giving up in case of liveness probe means restarting the container. In case of readiness probe the Pod will be marked Unready.
 Defaults to 3. Minimum value is 1.
 
+{{< note >}}
+Before Kubernetes 1.20, the field `timeoutSeconds` was not respected for exec probes:
+probes continued running indefinitely, even past their configured deadline,
+until a result was returned.
+
+This defect was corrected in Kubernetes v1.20. You may have been relying on the previous behavior,
+even without realizing it, as the default timeout is 1 second.
+As a cluster administrator, you can disable the [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) `ExecProbeTimeout` (set it to `false`)
+on each kubelet to restore the  behavior from older versions, then remove that override
+once all the exec probes in the cluster have a `timeoutSeconds` value set.  
+If you have pods that are impacted from the default 1 second timeout,
+you should update their probe timeout so that you're ready for the
+eventual removal of that feature gate.
+
+With the fix of the defect, for exec probes, on Kubernetes `1.20+` with the `dockershim` container runtime,
+the process inside the container may keep running even after probe returned failure because of the timeout.
+{{< /note >}}
+{{< caution >}}
+Incorrect implementation of readiness probes may result in an ever growing number
+of processes in the container, and resource starvation if this is left unchecked.
+{{< /caution >}}
+
 ### HTTP probes
 
 [HTTP probes](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#httpgetaction-v1-core)
@@ -406,7 +428,3 @@ You can also read the API references for:
 * [Pod](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#pod-v1-core)
 * [Container](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#container-v1-core)
 * [Probe](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#probe-v1-core)
-
-
-
-