Kubernetes: Command and Arguments in Pod

The command and args fields in Kubernetes Pod YAML files specify the command to be run in the container and any additional arguments to be passed to the command, respectively. The command field corresponds to the ENTRYPOINT instruction in a Dockerfile, while the args field corresponds to the CMD instruction. By specifying these fields, you can customize the command and arguments that are executed in the container, giving you flexibility to run any command in the container.

Kubernetes: Command and Arguments in Pod

Table of Contents

· command and args in Pod YAML
· Dockerfile vs. Pod YAML
  ∘ ENTRYPOINT(Docker) vs. command(Pod YAML)
  ∘ CMD(Docker) vs. args(Pod YAML)
  ∘ Example

command and args in Pod YAML

command and args in Pod YAML

To specify the command and arguments that should be executed within a Pod, you can define them in the Pod’s YAML file using the command and args fields.

The command field is used to specify the command to be run in the container. The command can be specified as an array of strings, where each string in the array represents a part of the command.

The args field is used to specify any additional arguments to be passed to the command specified in the command field. The arguments can also be specified as an array of strings.

pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
  - name: my-container
    image: my-image
    command: ["echo", "Hello"]
    args: ["world"]

In this example, the command field specifies that the command to be run in the container should be echo "Hello". The args field specifies that the argument to be passed to the command is world.

So, when this Pod is started, it will run the command echo "Hello" world, which will output Hello world in the container.

You can also specify command and args using multiple lines :

command:
- "echo"
- "Hello"
args:
- "world"

Dockerfile vs. Pod YAML

ENTRYPOINT and CMD instruction in a Dockerfile corresponds to command and args field in a Pod YAML file, respectively.

Dockerfile vs. Pod YAML

ENTRYPOINT(Docker) vs. command(Pod YAML)

In a Dockerfile, the ENTRYPOINT instruction specifies the command that will be run when a container starts.

In a Kubernetes Pod YAML file, the command field specifies the command to be run in the container.

CMD(Docker) vs. args(Pod YAML)

In a Dockerfile, the CMD instruction specifies the default arguments that will be passed to the ENTRYPOINT command if no arguments are specified when the container is started.

In a Kubernetes Pod YAML file, the args field specifies the arguments to be passed to the command specified in the command field.

Example

Dockerfile

FROM alpine
ENTRYPOINT ["echo", "Hello"]
CMD ["world"]

pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
  - name: my-container
    image: my-image
    command: ["echo", "Hello"]
    args: ["world"]

In this example, the ENTRYPOINT instruction in the Dockerfile sets the command to be echo "Hello", while the CMD instruction specifies that the default argument should be world.

In the Pod YAML file, the command field specifies the command to be echo "Hello", while the args field specifies that the argument should be world. When this Pod is started, it will run the command echo "Hello" world, which will output Hello world in the container.

These are my personal notes for CKA exam preparation on Kubernetes. Please feel free to correct me if you notice any errors. 😊

Related Story

• Kubernetes: Pods

Reference:

Define a Command and Arguments for a Container