[SOLVED] When should I use commands or args in readinessProbes

When should I use commands or args in readinessProbes

I am working my way through killer.sh.for the CKAD. I encountered a pod definition file that has a command field under the readiness probe and the container executes another command but uses args.

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: pod6
  name: pod6
spec:
  containers:
  - args:
    - sh
    - -c
    - touch /tmp/ready && sleep 1d
    image: busybox:1.31.0
    name: pod6
    resources: {}
    readinessProbe:                             # add
      exec:                                     # add
        command:                                # add
        - sh                                    # add
        - -c                                    # add
        - cat /tmp/ready                        # add
      initialDelaySeconds: 5                    # add
      periodSeconds: 10                         # add
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

If the readiness probe weren't used and this pod were created implicitly, args wouldn't be utilized.

kubectl run pod6 --image=busybox:1.31.0 --dry-run=client --command -- sh -c "touch /tmp/ready && sleep 1d" > 6.yaml

The output YAML would look like this:

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: pod69
  name: pod69
spec:
  containers:
  - command:
    - sh
    - -c
    - touch /tmp/ready && sleep 1d
    image: busybox:1.31.9
    name: pod69
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always

Why is command not used on both the readinessProbe and the container? When do commands become args? Is there a way to tell?

I've read through this document: https://kubernetes.io/docs/tasks/inject-data-application/_print/ but I still haven't had much luck understanding this situation and when to switch to args.

Solution

The reason why you have both cmd + args in Kubernetes is because it gives you options to override the default Commands + Args from the image that you are trying to run. In your specific case, the busybox image does not have any default Commands with the image so specifying the starting command in either cmd or args in the Pod.yaml file is essentially the same. To your question of when do commands become args - they dont, when a container is spun up using your image, it simply executes cmd + args. And if the cmd is empty in (both the image & the yaml file) then only the args are executed.

The thread here may give you some more explanation