VolumeSubpathEnvExpansion alpha feature

content/en/docs/concepts/storage/volumes.md

@@ -1017,6 +1017,51 @@ spec:
         claimName: my-lamp-site-data
 ```
 
+### Using subPath with expanded environment variables
+
+{{< feature-state for_k8s_version="v1.11" state="alpha" >}}
+
+
+
+You can use expanded environment variables in a subPath value. `subPath` directory names can also
+be constructed from Downward API environment variables. Before you use this feature, you must enable
+the `VolumeSubpathEnvExpansion`feature gate.
+
+In this example, a Pod uses `subPath` to create a directory within `/logs/pod1/`, using
+the pod name. That directory is mounted at `/logs/` within the container. 
+
+From the container's point of view, logs are stored in `/logs/`, so the command does not need to change, but in the volume, each Pod will get its own separate log directory.
+
+
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+  name: pod1
+spec:
+  containers:
+  - name: container1
+    env:
+    - name: POD_NAME
+      valueFrom:
+        fieldRef:
+          apiVersion: v1
+          fieldPath: metadata.name
+    image: busybox
+    command: [ "sh", "-c", "while [ true ]; do echo 'Hello'; sleep 10; done | tee -a /logs/hello.txt" ]
+    volumeMounts:
+    - name: workdir1
+      mountPath: /logs
+      subPath: $(POD_NAME)
+  restartPolicy: Never
+  volumes:
+  - name: workdir1
+    hostPath: 
+      path: /var/log/pods
+```
+
+On the host, the logs are written to `/var/log/pods/pod1/hello.txt`
+
 ## Resources
 
 The storage media (Disk, SSD, etc.) of an `emptyDir` volume is determined by the

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

@@ -93,6 +93,7 @@ different Kubernetes components.
 | `TokenRequest` | `false` | Alpha | 1.10 | |
 | `VolumeScheduling` | `false` | Alpha | 1.9 | 1.9 |
 | `VolumeScheduling` | `true` | Beta | 1.10 | |
+| `VolumeSubpathEnvExpansion` | `false` | Alpha | 1.11 | |
 
 ## Using a Feature