Document ephemeral containers feature for 1.16 (#15994)

Also, I've snuck in a trivial update for the ShareProcessNamespace
feature gate, adding an "Until" version which had been omitted.

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

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

@@ -82,7 +82,6 @@ different Kubernetes components.
 | `CustomResourceValidation` | `true` | Beta | 1.9 | |
 | `CustomResourceWebhookConversion` | `false` | Alpha | 1.13 | 1.14 |
 | `CustomResourceWebhookConversion` | `true` | Beta | 1.15 | |
-| `DebugContainers` | `false` | Alpha | 1.10 | |
 | `DevicePlugins` | `false` | Alpha | 1.8 | 1.9 |
 | `DevicePlugins` | `true` | Beta | 1.10 | |
 | `DryRun` | `true` | Beta | 1.13 | |
@@ -93,6 +92,7 @@ different Kubernetes components.
 | `DynamicVolumeProvisioning` | `true` | Alpha | 1.3 | 1.7 |
 | `DynamicVolumeProvisioning` | `true` | GA | 1.8 | |
 | `EnableEquivalenceClassCache` | `false` | Alpha | 1.8 | |
+| `EphemeralContainers` | `false` | Alpha | 1.16 | |
 | `ExpandCSIVolumes` | `false` | Alpha | 1.14 | |
 | `ExpandInUsePersistentVolumes` | `false` | Alpha | 1.11 | 1.14 |
 | `ExpandInUsePersistentVolumes` | `true` | Beta | 1.15 | |
@@ -135,7 +135,7 @@ different Kubernetes components.
 | `PodReadinessGates` | `false` | Alpha | 1.11 | 1.11 |
 | `PodReadinessGates` | `true` | Beta | 1.12 | 1.13 |
 | `PodReadinessGates` | `true` | GA | 1.14 | - |
-| `PodShareProcessNamespace` | `false` | Alpha | 1.10 | |
+| `PodShareProcessNamespace` | `false` | Alpha | 1.10 | 1.11 |
 | `PodShareProcessNamespace` | `true` | Beta | 1.12 | |
 | `ProcMountType` | `false` | Alpha | 1.12 | |
 | `PVCProtection` | `false` | Alpha | 1.9 | 1.9 |
@@ -278,7 +278,6 @@ Each feature gate is designed for enabling/disabling a specific feature:
   [CustomResourceDefinition](/docs/concepts/api-extension/custom-resources/).
 - `CustomResourceWebhookConversion`: Enable webhook-based conversion
   on resources created from [CustomResourceDefinition](/docs/concepts/api-extension/custom-resources/).
-- `DebugContainers`: Enable running a "debugging" container in a Pod's namespace to
   troubleshoot a running Pod.
 - `DevicePlugins`: Enable the [device-plugins](/docs/concepts/cluster-administration/device-plugins/)
   based resource provisioning on nodes.
@@ -289,6 +288,8 @@ Each feature gate is designed for enabling/disabling a specific feature:
   This feature is superceded by the `VolumeScheduling` feature completely in v1.12.
 - `DynamicVolumeProvisioning`(*deprecated*): Enable the [dynamic provisioning](/docs/concepts/storage/dynamic-provisioning/) of persistent volumes to Pods.
 - `EnableEquivalenceClassCache`: Enable the scheduler to cache equivalence of nodes when scheduling Pods.
+- `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 [Even Pods Spread](/docs/concepts/configuration/even-pods-spread).
 - `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).
@@ -319,8 +320,11 @@ Each feature gate is designed for enabling/disabling a specific feature:
 - `PodOverhead`: Enable the [PodOverhead](/docs/concepts/configuration/pod-overhead/) feature to account for pod overheads.
 - `PodPriority`: Enable the descheduling and preemption of Pods based on their [priorities](/docs/concepts/configuration/pod-priority-preemption/).
 - `PodReadinessGates`: Enable the setting of `PodReadinessGate` field for extending
-  Pod readiness evaluation.
-  For more details, please see [Pod readiness gate](/docs/concepts/workloads/pods/pod-lifecycle/#pod-readiness-gate).
+  Pod readiness evaluation.  See [Pod readiness gate](/docs/concepts/workloads/pods/pod-lifecycle/#pod-readiness-gate)
+  for more details.
+- `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/).
 - `ProcMountType`: Enables control over ProcMountType for containers.
 - `PVCProtection`: Enable the prevention of a PersistentVolumeClaim (PVC) from
   being deleted when it is still used by any Pod.

content/en/docs/reference/glossary/ephemeral-container.md

@@ -0,0 +1,18 @@
+---
+title: Ephemeral Container
+id: ephemeral-container
+date: 2019-08-26
+full_link: /docs/concepts/workloads/pods/ephemeral-containers/
+short_description: >
+  A type of container type that you can temporarily run inside a Pod
+
+aka:
+tags:
+- fundamental
+---
+A {{< glossary_tooltip term_id="container" >}} type that you can temporarily run inside a {{< glossary_tooltip term_id="pod" >}}.
+
+<!--more-->
+
+If you want to investigate a Pod that's running with problems, you can add an ephemeral container to that Pod and carry out diagnostics. Ephemeral containers have no resource or scheduling guarantees, and you should not use them to run any part of the workload itself.
+