Merge branch 'master' into toc-updates

_data/tasks.yml

@@ -12,6 +12,7 @@ toc:
   - docs/tasks/configure-pod-container/distribute-credentials-secure.md
   - docs/tasks/configure-pod-container/pull-image-private-registry.md
   - docs/tasks/configure-pod-container/configure-liveness-readiness-probes.md
+  - docs/tasks/configure-pod-container/communicate-containers-same-pod.md
 
 - title: Accessing Applications in a Cluster
   section:

docs/tasks/configure-pod-container/communicate-containers-same-pod.md

@@ -0,0 +1,149 @@
+---
+title: Communicating Between Containers Running in the Same Pod
+---
+
+{% capture overview %}
+
+This page shows how to use a Volume to communicate between two Containers running
+in the same Pod.
+
+{% endcapture %}
+
+
+{% capture prerequisites %}
+
+{% include task-tutorial-prereqs.md %}
+
+{% endcapture %}
+
+
+{% capture steps %}
+
+###  Creating a Pod that runs two Containers
+
+In this exercise, you create a Pod that runs two Containers. The two containers
+share a Volume that they can use to communicate. Here is the configuration file
+for the Pod:
+
+{% include code.html language="yaml" file="two-container-pod.yaml" ghlink="/docs/tasks/configure-pod-container/two-container-pod.yaml" %}
+
+In the configuration file, you can see that the Pod has a Volume named
+`shared-data`.
+
+The first container listed in the configuration file runs an nginx server. The
+mount path for the shared Volume is `/usr/share/nginx/html`.
+The second container is based on the debian image, and has a mount path of
+`/pod-data`. The second container runs the following command and then terminates.
+
+    echo Hello from the debian container > /pod-data/index.html
+
+Notice that the second container writes the `index.html` file in the root
+directory of the nginx server.
+
+Create the Pod and the two Containers:
+
+    kubectl create -f http://k8s.io/docs/tasks/configure-pod-container/two-container-pod.yaml
+
+View information about the Pod and the Containers:
+
+    kubectl get pod two-containers --output=yaml
+
+Here is a portion of the output:
+
+    apiVersion: v1
+    kind: Pod
+    metadata:
+      ...
+      name: two-containers
+      namespace: default
+      ...
+    spec:
+      ...
+      containerStatuses:
+
+      - containerID: docker://c1d8abd1 ...
+        image: debian
+        ...
+        lastState:
+          terminated:
+            ...
+        name: debian-container
+        ...
+
+      - containerID: docker://96c1ff2c5bb ...
+        image: nginx
+        ...
+        name: nginx-container
+        ...
+        state:
+          running:
+        ...
+
+You can see that the debian Container has terminated, and the nginx Container
+is still running.
+
+Get a shell to nginx Container:
+
+    kubectl exec -it two-containers -c nginx-container -- /bin/bash
+
+In your shell, verify that nginx is running:
+
+    root@two-containers:/# ps aux
+
+The output is similar to this:
+
+    USER       PID  ...  STAT START   TIME COMMAND
+    root         1  ...  Ss   21:12   0:00 nginx: master process nginx -g daemon off;
+
+Recall that the debian Container created the `index.html` file in the nginx root
+directory. Use `curl` to send a GET request to the nginx server:
+
+    root@two-containers:/# apt-get update
+    root@two-containers:/# apt-get install curl
+    root@two-containers:/# curl localhost
+
+The output shows that nginx serves a web page written by the debian container:
+
+    Hello from the debian container
+
+{% endcapture %}
+
+
+{% capture discussion %}
+
+### Discussion
+
+The primary reason that Pods can have multiple containers is to support
+helper applications that assist a primary application. Typical examples of
+helper applications are data pullers, data pushers, and proxies.
+Helper and primary applications often need to communicate with each other.
+Typically this is done through a shared filesystem, as shown in this exercise,
+or through the loopback network interface, localhost. An example of this pattern is a
+web server along with a helper program that polls a Git repository for new updates.
+
+The Volume in this exercise provides a way for Containers to communicate during
+the life of the Pod. If the Pod is deleted and recreated, any data stored in
+the shared Volume is lost.
+
+{% endcapture %}
+
+
+{% capture whatsnext %}
+
+* Learn more about
+[patterns for composite containers](http://blog.kubernetes.io/2015/06/the-distributed-system-toolkit-patterns.html).
+
+* Learn about
+[composite containers for modular architecture](http://www.slideshare.net/Docker/slideshare-burns).
+
+* See
+[Configuring a Pod to Use a Volume for Storage](http://localhost:4000/docs/tasks/configure-pod-container/configure-volume-storage/).
+
+* See [Volume](/docs/api-reference/v1/definitions/#_v1_volume).
+
+* See [Pod](/docs/api-reference/v1/definitions/#_v1_pod).
+
+{% endcapture %}
+
+
+{% include templates/task.md %}

docs/tasks/configure-pod-container/two-container-pod.yaml

@@ -0,0 +1,27 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: two-containers
+spec:
+
+  restartPolicy: Never
+
+  volumes:
+  - name: shared-data
+    emptyDir: {}
+
+  containers:
+
+  - name: nginx-container
+    image: nginx
+    volumeMounts:
+    - name: shared-data
+      mountPath: /usr/share/nginx/html
+
+  - name: debian-container
+    image: debian
+    volumeMounts:
+    - name: shared-data
+      mountPath: /pod-data
+    command: ["/bin/sh"]
+    args: ["-c", "echo Hello from the debian container > /pod-data/index.html"]