task-033-commands-and-arguments

Commands And Arguments

• Suppose you want to run the following command in kubernetes pod: ls -ltrh

apiVersion: v1
kind: Pod
metadata:
  name: ubuntu
spec:
  containers:
  - name: ubuntu-container
    image: ubuntu
    command: ["ls"]
    args: ["-ltrh"]

• Apply

$ kubectl apply -f pod-ubuntu-ls.yaml  
pod/ubuntu created

$ kubectl get pods
NAME     READY   STATUS              RESTARTS   AGE
ubuntu   0/1     ContainerCreating   0          12s

$ kubectl get pods
NAME     READY   STATUS      RESTARTS   AGE
ubuntu   0/1     Completed   0          15s

$ kubectl get pods
NAME     READY   STATUS             RESTARTS   AGE
ubuntu   0/1     CrashLoopBackOff   1          17s

$ kubectl logs -f ubuntu                                         
total 48K
drwxr-xr-x   2 root root 4.0K Apr 15  2020 home
drwxr-xr-x   2 root root 4.0K Apr 15  2020 boot
lrwxrwxrwx   1 root root    8 Nov  6 01:21 sbin -> usr/sbin
lrwxrwxrwx   1 root root   10 Nov  6 01:21 libx32 -> usr/libx32
lrwxrwxrwx   1 root root    9 Nov  6 01:21 lib64 -> usr/lib64
lrwxrwxrwx   1 root root    9 Nov  6 01:21 lib32 -> usr/lib32
lrwxrwxrwx   1 root root    7 Nov  6 01:21 lib -> usr/lib
lrwxrwxrwx   1 root root    7 Nov  6 01:21 bin -> usr/bin
drwxr-xr-x   1 root root 4.0K Nov  6 01:21 usr
drwxr-xr-x   2 root root 4.0K Nov  6 01:21 srv
drwxr-xr-x   2 root root 4.0K Nov  6 01:21 opt
drwxr-xr-x   2 root root 4.0K Nov  6 01:21 mnt
drwxr-xr-x   2 root root 4.0K Nov  6 01:21 media
drwxr-xr-x   1 root root 4.0K Nov  6 01:25 var
drwx------   2 root root 4.0K Nov  6 01:25 root
drwxrwxrwt   2 root root 4.0K Nov  6 01:25 tmp
dr-xr-xr-x  13 root root    0 Jan 15 09:35 sys
drwxr-xr-x   1 root root 4.0K Jan 15 09:35 etc
dr-xr-xr-x 206 root root    0 Jan 15 09:35 proc
drwxr-xr-x   1 root root 4.0K Jan 15 09:35 run
drwxr-xr-x   5 root root  360 Jan 15 09:35 dev

• Note it goes to CrashLoopBack as the container exits after the command is run. And kubernetes tries to restart the pod as the container has exited

What is the command used to run the pod 'ubuntu-sleeper'?

$ kubectl describe pod ubuntu-sleeper | grep -A 3 -i command
    Command:
      sleep
      4800
    State:          Running

Create a pod with the ubuntu image to run a container to sleep for 5000 seconds.

controlplane $ kubectl apply -f ubuntu-sleeper-2.yaml
pod/ubuntu-sleeper-2 created
controlplane $ cat ubuntu-sleeper-2.yaml
apiVersion: v1
kind: Pod
metadata:
  name: ubuntu-sleeper-2
spec:
  containers:
  - name: ubuntu
    image: ubuntu
    command: ["sleep"]
    args: ["5000"]

##### OR 
controlplane $ cat ubuntu-sleeper-3.yaml
apiVersion: v1
kind: Pod
metadata:
  name: ubuntu-sleeper-3
spec:
  containers:
  - name: ubuntu
    image: ubuntu
    command:
      - "sleep"
      - "5000"

Suppose you have the following Dockerfile given

controlplane $ cat Dockerfile
FROM python:3.6-alpine

RUN pip install flask

COPY . /opt/

EXPOSE 8080

WORKDIR /opt

ENTRYPOINT ["python", "app.py"]

What is the command used at startup

python app.py

controlplane $ cat Dockerfile2
FROM python:3.6-alpine

RUN pip install flask

COPY . /opt/

EXPOSE 8080

WORKDIR /opt

ENTRYPOINT ["python", "app.py"]

CMD ["--color", "red"]

What is the command for above Dockerfile

python app.py --color red

Inspect the two files and tell what command is run at container startup?

controlplane $ cat Dockerfile2
FROM python:3.6-alpine

RUN pip install flask

COPY . /opt/

EXPOSE 8080

WORKDIR /opt

ENTRYPOINT ["python", "app.py"]

CMD ["--color", "red"]

controlplane $ cat webapp-color-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: webapp-green
  labels:
      name: webapp-green
spec:
  containers:
  - name: simple-webapp
    image: kodekloud/webapp-color
    command: ["--color","green"]
controlplane $

--color green

Inspect the two files and tell What command is run at container startup?

controlplane $ cat Dockerfile2
FROM python:3.6-alpine

RUN pip install flask

COPY . /opt/

EXPOSE 8080

WORKDIR /opt

ENTRYPOINT ["python", "app.py"]

CMD ["--color", "red"]

controlplane $ cat webapp-color-pod-2.yaml
apiVersion: v1
kind: Pod
metadata:
  name: webapp-green
  labels:
      name: webapp-green
spec:
  containers:
  - name: simple-webapp
    image: kodekloud/webapp-color
    command: ["python", "app.py"]
    args: ["--color", "pink"]

python app.py --color pink

Create a pod with the given specifications. By default it displays a 'blue' background. Set the given command line arguments to change it to 'green'

• Pod Name: webapp-green
• Image: kodekloud/webapp-color
• Command line arguments: --color=green

controlplane $ kubectl run nginx-pod --image=nginx --dry-run=client -o yaml > pod.yaml
controlplane $ vi pod.yaml
controlplane $ kubectl apply -f pod.yaml
pod/webapp-green created
controlplane $ cat pod.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: my-pod
  name: webapp-green
spec:
  containers:
  - image: kodekloud/webapp-color
    name: webapp-green-container
    command: ["python", "app.py"]
    args: ["--color", "green"]    
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}