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In this tutorial, you’ll learn how to configure commands and arguments in a Kubernetes Pod. We’ll use a simple ubuntu-sleeper image that demonstrates how ENTRYPOINT and CMD from a Dockerfile map to the command and args fields in a Pod spec.

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Table of Contents

  1. Recap: ubuntu-sleeper Docker Image
  2. Create a Pod with the Default Command
  3. Override CMD with args
  4. Override ENTRYPOINT with command
  5. Summary & Mapping Table
  6. References

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Recap: ubuntu-sleeper Docker Image

We built a minimal Docker image called ubuntu-sleeper: 
FROM ubuntu
ENTRYPOINT ["sleep"]
CMD ["5"]
  • Running without extra arguments uses the default sleep duration (5 seconds): 
    docker run --name ubuntu-sleeper ubuntu-sleeper
  • Providing an argument overrides CMD (for example, sleep 10): 
    docker run --name ubuntu-sleeper ubuntu-sleeper 10
In Docker CLI, anything after the image name replaces the CMD instruction.

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Create a Pod with the Default Command

Here’s the simplest Pod manifest that runs sleep 5 by default: 
apiVersion: v1
kind: Pod
metadata:
  name: ubuntu-sleeper-pod
spec:
  containers:
    - name: ubuntu-sleeper
      image: ubuntu-sleeper
Apply the Pod: 
kubectl create -f pod-definition.yml
By default, Kubernetes uses the image’s ENTRYPOINT + CMD (sleep 5), and the container will exit after 5 seconds.

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Override CMD with args

To change the sleep duration without touching the entrypoint, specify an args array in your Pod spec: 
apiVersion: v1
kind: Pod
metadata:
  name: ubuntu-sleeper-pod
spec:
  containers:
    - name: ubuntu-sleeper
      image: ubuntu-sleeper
      args: ["10"]
This runs sleep 10. Update the Pod: 
kubectl apply -f pod-definition.yml
The args field in Kubernetes corresponds directly to the Dockerfile CMD. Any elements you list here will override the default CMD values.

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Override ENTRYPOINT with command

If you need to override both the entrypoint and its arguments, use the command field for the entrypoint and args for its parameters: 
apiVersion: v1
kind: Pod
metadata:
  name: ubuntu-sleeper-pod
spec:
  containers:
    - name: ubuntu-sleeper
      image: ubuntu-sleeper
      command: ["sleep2.0"]
      args: ["10"]
  • command replaces the Dockerfile ENTRYPOINT.
  • args replaces the Dockerfile CMD.
Apply this configuration: 
kubectl create -f pod-definition.yml
If you override the command field, make sure the specified executable exists in the container filesystem. Otherwise, the Pod will fail to start.

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Summary & Mapping Table

The table below summarizes how Dockerfile instructions map to Kubernetes Pod spec fields:
Dockerfile InstructionKubernetes Pod Spec FieldPurpose
ENTRYPOINTcommandDefines the executable to run
CMDargsProvides default parameters/arguments
Use these fields to precisely control the process invoked inside your containers.

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References

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