Kubernetes - Commands and Arguments 🔣

Description 👀

To pass arguments to a container, you can use the args field of the container spec. Arguments to the entrypoint can be passed using the command field of the container spec.

• example container cmd-and-args-example/Dockerfile
• example pod definition cmd-and-args-example/pod-definition.yaml

Docker Commands and Arguments 🐳

• generic DOCKERFILE template

  FROM <image>
  RUN <command>
  CMD <command>
  

• commands template with parameters

  CMD command param
  CMD ["command", "param"]
  

• example command with arguments

  CMD sleep 5
  CMD ["sleep", "5"]
  

• makes a custom image of ubuntu and makes it sleep 5 seconds then exits

  FROM Ubuntu
  CMD sleep 5
  

• makes a custom image of ubuntu and makes it sleep from passed in param in entrypoint
  • entrypoint is the command that is run when the container is started

  FROM Ubuntu
  ENTRYPOINT ["sleep"]
  

• makes a custom image of ubuntu and makes it sleep from passed in param in entrypoint with default of 5 seconds

  FROM Ubuntu
  ENTRYPOINT ["sleep"]
  CMD ["5"]
  

  • you can override the entrypoint command with the –entrypoint flag

• Docker Security 🔒

  • to run docker as a non-root user

    docker run --user=<user id> <image>
    

  • users can also be defined in the dockerfile

    FROM ubuntu
    USER <user id>
    

Examples 🧩

• sample Dockerfile 🐳

    FROM ubuntu
    ENTRYPOINT [ "sleep" ]
    CMD [ "5" ]
  

• sample pod definition with container commands and arguments

    apiVersion: v1
    kind: Pod
    metadata:
        name: ubuntu-sleeper-pod
    spec:
        containers:
          - image: ubuntu-sleeper
            name: ubuntu-sleeper
            # overrides the entrypoint instruction 
            command: ["echo"]  
            # overrieds the commad instruction  
            args: ["10"]
  

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