This page shows how to define commands and arguments when you run a container in a Kubernetes Pod.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube.
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
field in the configuration file. To define arguments for the command, include
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.
In this exercise, you create a Pod that runs one container. The configuration file for the Pod defines a command and two arguments:
Create a Pod based on the YAML configuration file:
kubectl create -f https://k8s.io/docs/tasks/inject-data-application/commands.yaml
List the running Pods:
kubectl get pods
The output shows that the container that ran in the command-demo Pod has completed.
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:
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: ["$(MESSAGE)"]
NOTE: The environment variable appears in parentheses,
"$(VAR)". This is
required for the variable to be expanded in the
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"]
This table summarizes the field names used by Docker and Kubernetes.
|Description||Docker field name||Kubernetes field name|
|The command run by the container||Entrypoint||command|
|The arguments passed to the command||Cmd||args|
When you override the default Entrypoint and Cmd, these rules apply:
If you do not supply
args for a Container, the defaults defined
in the Docker image are used.
If you supply a
command but no
args for a Container, only the supplied
command is used. The default EntryPoint and the default Cmd defined in the Docker
image are ignored.
If you supply only
args for a Container, the default Entrypoint defined in
the Docker image is run with the
args that you supplied.
If you supply a
args, the default Entrypoint and the default
Cmd defined in the Docker image are ignored. Your
command is run with your
Here are some examples:
|Image Entrypoint||Image Cmd||Container command||Container args||Command run|
||<not set>||<not set>||