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pod-command-args.md

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Create POD with Command and Arguments
Kubectl explain pod
Create-POD-with-Command-and-Arguments
9

kubectl explain pods.spec.containers.command

k8s101 git:(main) ✗ kubectl explain pods.spec.containers.command  
KIND:     Pod
VERSION:  v1

FIELD:    command <[]string>

DESCRIPTION:
     Entrypoint array. Not executed within a shell. The container image's
     ENTRYPOINT is used if this is not provided. Variable references $(VAR_NAME)
     are expanded using the container's environment. If a variable cannot be
     resolved, the reference in the input string will be unchanged. Double $$
     are reduced to a single $, which allows for escaping the $(VAR_NAME)
     syntax: i.e. "$$(VAR_NAME)" will produce the string literal "$(VAR_NAME)".
     Escaped references will never be expanded, regardless of whether the
     variable exists or not. Cannot be updated. More info:
     https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#running-a-command-in-a-shell
➜  k8s101 git:(main) ✗

Create POD without any commands or arguments.

args in Kubernetes overrides CMD in the original docker image. command in Kubernetes overrides ENTRYPOINT in the original docker image.

commands.yaml
apiVersion: v1
kind: Pod
metadata:
  name: command
spec:
  containers:
  -  image: busybox
     name: count
➜  k8s101 git:(main) ✗ kubectl apply -f commands.yaml
pod/command created
➜  k8s101 git:(main) ✗ kubectl get pods
NAME         READY   STATUS             RESTARTS     AGE
command      0/1     CrashLoopBackOff   1 (5s ago)   15s
nginx-pod    1/1     Running            0            50m
nginx-port   1/1     Running            0            156m
webserver    1/1     Running            0            34m
➜  k8s101 git:(main) ✗ kubectl exec -it command -- bash

Create POD with Command

Modify the POD contents to the following one.

apiVersion: v1
kind: Pod
metadata:
  name: command2
spec:
  containers:
  -  image: busybox
     name: count
     command: ["sleep","3600"]
➜  k8s101 git:(main) ✗ kubectl apply -f commands.yaml
pod/command2 created
➜  k8s101 git:(main) ✗ kubectl get pods
NAME       READY   STATUS    RESTARTS   AGE
command    1/1     Running   0          67s
➜  k8s101 git:(main) ✗ kubectl exec -it command2 -- sh
/ # ls
bin    dev    etc    home   lib    lib64  proc   root   sys    tmp    usr    var
/ #

Create POD with Command and Arguments

Modify the YAML file contents to the following one.

apiVersion: v1
kind: Pod
metadata:
  name: command3
spec:
  containers:
  -  image: busybox
     name: count
     command: ["sleep"]
     args: ["3600"]
➜  k8s101 git:(main) ✗ kubectl apply -f commands.yaml 
pod/command3 created
➜  k8s101 git:(main) ✗ kubectl get pods
NAME       READY   STATUS    RESTARTS   AGE
command    1/1     Running   0          3m18s
command2   1/1     Running   0          2m34s
command3   1/1     Running   0          14s

Create POD with Arguments

Modify the YAML file contents to the following one.

apiVersion: v1
kind: Pod
metadata:
  name: command3
spec:
  containers:
  - name: command3
    image: debian
    command: ["printenv"]
    args: ["HOSTNAME", "KUBERNETES_PORT"]
➜  k8s101 git:(main) ✗ kubectl apply -f commands.yaml
➜  k8s101 git:(main) ✗ kubectl get pods
➜  k8s101 git:(main) ✗ kubectl logs command3    
command3
tcp://10.96.0.1:443