Commands and Arguments

Commands, here, will refer to the command that a docker container runs on startup.
A node server might run npm run server if it were using npm to run the server, or node server.js if it were using node directly.

Arguments, here, will refer to any, well, arguments passed to the command(s) that are run when a docker container is run.
A node server may expect a db connection name as DB_NAME=<db-name-here> and will be expecting it after the node run command, like this -> node index.js DB_NAME="pg-box".

• Commands and Arguments
  • Modify a pod definition file to have a new command
    • Use a list to describe commands in a pod definition
  • Mapping between Pod Definitions and COntainer Definitions

Modify a pod definition file to have a new command

Make this ubuntu image sleep for 10K seconds

# pod-def-1.yaml
apiVersion: v1
kind: Pod
metadata:
  name: tired-ubuntu
spec:
  containers:
    - name: ubuntu
      image: ubuntu
    # THIS can get added to make the machine sleep for 10,000 seconds
      command: ["sleep", "10000"]

Use a list to describe commands in a pod definition

Same def file as above, just expressed differently

# pod-def-1.yaml
apiVersion: v1
kind: Pod
metadata:
  name: tired-ubuntu
spec:
  containers:
    - name: ubuntu
      image: ubuntu
      command: 
        - "sleep"
        # NOTE these must be strings, not numbers
        - "10000"

Mapping between Pod Definitions and COntainer Definitions

• Containers use
  • ENTRYPOINT to define the command that is run
    • i.e ENTRYPOINT ["node", "."]
  • CMD to define arguments passed to the entrypoint command
  • i.e CMD ["DB_NAME", "PG_DB", "REDIS_NAME", "REDIS_BOX"]
• K8s Pod Def files, though, use different words to override the same things...
  • command to override the ENTRYPOINT of a dockerfile
    • i.e command: npm run start instead of node . above
  • args to override the CMD of a dockerfile
    • i.e args: ["DB_NAME", "HORSE", "REDIS_NAME", "DOG"] instead of above CMD args