Kubernetes - Trying to create pod with init container - docker

Question

I am trying to play with init pods. I want to use init container to create file and default container to check if file exist and sleep for a while.
my yaml:
apiVersion: v1
kind: Pod
metadata:
name: init-test-pod
spec:
containers:
- name: myapp-container
image: alpine
command: ['sh', '-c', 'if [ -e /workdir/test.txt ]; then sleep 99999; fi']
initContainers:
- name: init-myservice
image: busybox:1.28
command: ['sh', '-c', 'mkdir /workdir; echo>/workdir/test.txt']
When I am trying to debug from alpine image I use the command to create:
kubectl run alpine --rm -ti --image=alpine /bin/sh
If you don't see a command prompt, try pressing enter.
/ # if [ -e /workdir/test.txt ]; then sleep 3; fi
/ # mkdir /workdir; echo>/workdir/test.txt
/ # if [ -e /workdir/test.txt ]; then sleep 3; fi
/ *here shell sleeps for 3 seconds
/ #
And it seems like commands working as expected.
But on my real k8s cluster I have only CrashLoopBackOff for main container.
kubectl describe pod init-test-pod
Shows me only that error:
Containers:
myapp-container:
Container ID: docker://xxx
Image: alpine
Image ID: docker-pullable://alpine#sha256:xxx
Port: <none>
Host Port: <none>
Command:
sh
-c
if [ -e /workdir/test.txt ]; then sleep 99999; fi
State: Waiting
Reason: CrashLoopBackOff
Last State: Terminated
Reason: Completed
Exit Code: 0
Ready: False
Restart Count: 3
Environment: <none>

Answer 1

The problem here is that your main container is not finding the folder you create. When your initial container completes running, the folder gets wiped with it. You will need to use a Persistent Volume to be able to share the folder between the two containers:
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
name: mypvc
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
---
apiVersion: v1
kind: Pod
metadata:
name: init-test-pod
spec:
volumes:
- name: mypvc
persistentVolumeClaim:
claimName: mypvc
containers:
- name: myapp-container
image: alpine
command: ['sh', '-c', 'if [ -f /workdir/test.txt ]; then sleep 99999; fi']
volumeMounts:
- name: mypvc
mountPath: /workdir
initContainers:
- name: init-myservice
image: busybox:1.28
command: ['sh', '-c', 'mkdir /workdir; echo>/workdir/test.txt']
volumeMounts:
- name: mypvc
mountPath: /workdir
You can as well look at emptyDir, so you won't need the PVC:
apiVersion: v1
kind: Pod
metadata:
name: init-test-pod
spec:
volumes:
- name: mydir
emptyDir: {}
containers:
- name: myapp-container
image: alpine
command: ['sh', '-c', 'if [ -f /workdir/test.txt ]; then sleep 99999; fi']
volumeMounts:
- name: mydir
mountPath: /workdir
initContainers:
- name: init-myservice
image: busybox:1.28
command: ['sh', '-c', 'mkdir /workdir; echo>/workdir/test.txt']
volumeMounts:
- name: mydir
mountPath: /workdir

Answer 2

That's because your 2 containers have separate filesystems. You need to share this file using an emtyDir volume:
apiVersion: v1
kind: Pod
metadata:
name: init-test-pod
spec:
containers:
- name: myapp-container
image: alpine
command: ['sh', '-c', 'if [ -e /workdir/test.txt ]; then sleep 99999; fi']
volumeMounts:
- mountPath: /workdir
name: workdir
initContainers:
- name: init-myservice
image: busybox:1.28
command: ['sh', '-c', 'mkdir /workdir; echo>/workdir/test.txt']
volumeMounts:
- mountPath: /workdir
name: workdir
volumes:
- name: workdir
emptyDir: {}