Merge pull request #1526 from steveperry-53/task-cmd-arg

Write new task: Defining a Command and Arguments for a Container.

Author: Phillip Wittrock

_data/tasks.yml

@@ -6,6 +6,8 @@ toc:
   section:
   - title: Defining Environment Variables for a Container
     path: /docs/tasks/configure-pod-container/define-environment-variable-container/
+  - title: Defining a Command and Arguments for a Container
+    path: /docs/tasks/configure-pod-container/define-command-argument-container/
 - title: Accessing Applications in a Cluster
   section:
   - title: Using Port Forwarding to Access Applications in a Cluster

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

@@ -0,0 +1,12 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: command-demo
+  labels:
+    purpose: demonstrate-command
+spec:
+  containers:
+  - name: command-demo-container
+    image: debian
+    command: ["printenv"]
+    args: ["HOSTNAME", "KUBERNETES_PORT"]

docs/tasks/configure-pod-container/define-command-argument-container.md

@@ -0,0 +1,105 @@
+---
+---
+
+{% capture overview %}
+
+This page shows how to define commands and arguments when you run a container
+in a Kubernetes Pod.
+
+{% endcapture %}
+
+
+{% capture prerequisites %}
+
+{% include task-tutorial-prereqs.md %}
+
+{% endcapture %}
+
+
+{% capture steps %}
+
+### Defining a command and arguments when you create a Pod
+
+When you create a Pod, you can define a command and arguments for the
+containers that run in the Pod. To define a command, include the `command`
+field in the configuration file. To define arguments for the command, include
+the `args` field in the configuration file. The command and arguments that
+you define cannot be changed after the Pod is created.
+
+The command and arguments that you define in the configuration file
+override the default command and arguments provided by the container image.
+If you define args, but do not define a command, the default command is used
+with your new arguments. For more information, see
+[Commands and Capabilities](/docs/user-guide/containers/).
+
+In this exercise, you create a Pod that runs one container. The configuration
+file for the Pod defines a command and two arguments:
+
+{% include code.html language="yaml" file="commands.yaml" ghlink="/docs/tasks/configure-pod-container/commands.yaml" %}
+
+1. Create a Pod based on the YAML configuration file:
+
+        export REPO=https://raw.githubusercontent.com/kubernetes/kubernetes.github.io/master
+        kubectl create -f $REPO/docs/tasks/configure-pod-container/commands.yaml
+
+1. List the running Pods:
+
+        kubectl get pods
+
+    The output shows that the container that ran in the command-demo Pod has
+    completed.
+
+1. To see the output of the command that ran in the container, view the logs
+from the Pod:
+
+        kubectl logs command-demo
+
+    The output shows the values of the HOSTNAME and KUBERNETES_PORT environment
+    variables:
+
+        command-demo
+        tcp://10.3.240.1:443
+
+### Using environment variables to define arguments
+
+In the preceding example, you defined the arguments directly by
+providing strings. As an alternative to providing strings directly,
+you can define arguments by using environment variables:
+
+    env:
+    - name: MESSAGE
+      value: "hello world"
+    command: ["/bin/echo"]
+    args: ["$(MESSAGE)"]
+
+This means you can define an argument for a Pod using any of
+the techniques available for defining environment variables, including
+[ConfigMaps](/docs/user-guide/configmap/)
+and
+[Secrets](/docs/user-guide/secrets/).
+
+NOTE: The environment variable appears in parentheses, `"$(VAR)"`. This is
+required for the variable to be expanded in the `command` or `args` field.
+
+### Running a command in a shell
+
+In some cases, you need your command to run in a shell. For example, your
+command might consist of several commands piped together, or it might be a shell
+script. To run your command in a shell, wrap it like this:
+
+    command: ["/bin/sh"]
+    args: ["-c", "while true; do echo hello; sleep 10;done"]
+
+{% endcapture %}
+
+{% capture whatsnext %}
+
+* Learn more about [containers and commands](/docs/user-guide/containers/).
+* Learn more about [configuring containers](/docs/user-guide/configuring-containers/).
+* Learn more about [running commands in a container](/docs/user-guide/getting-into-containers/).
+* See [Container](/docs/api-reference/v1/definitions/#_v1_container).
+
+{% endcapture %}
+
+
+{% include templates/task.md %}

docs/tasks/index.md

@@ -3,6 +3,11 @@
 
 The Tasks section of the Kubernetes documentation is a work in progress
 
+#### Configuring Pods and Containers
+
+* [Defining Environment Variables for a Container](/docs/tasks/configure-pod-container/define-environment-variable-container/)
+* [Defining a Command and Arguments for a Container](/docs/tasks/configure-pod-container/define-command-argument-container/)
+
 #### Accessing Applications in a Cluster
 
 * [Using Port Forwarding to Access Applications in a Cluster](/docs/tasks/access-application-cluster/port-forward-access-application-cluster/)