Kubernetes initContainers to copy file and execute as part of Lifecycle Hook PostStart - kubernetes

Question

I am trying to execute some scripts as part of statefulset deployment kind. This script I have added as configmap and I use this as volumeMount inside the pod definition. I use the lifecycle poststart exec command to execute this script. It fails with the permission issue.
based on certain articles, I found that we should copy this file as part of InitContainer and then use that (I am not sure why should we do and what will make a difference)
Still, I tried it and that also gives the same error.
Here is my ConfigMap:
apiVersion: v1
kind: ConfigMap
metadata:
name: postgres-configmap-initscripts
data:
poststart.sh: |
#!/bin/bash
echo "It`s done"
Here is my StatefulSet:
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: postgres-statefulset
spec:
....
serviceName: postgres-service
replicas: 1
template:
...
spec:
initContainers:
- name: "postgres-ghost"
image: alpine
volumeMounts:
- mountPath: /scripts
name: postgres-scripts
containers:
- name: postgres
image: postgres
lifecycle:
postStart:
exec:
command: ["/bin/sh", "-c", "/scripts/poststart.sh" ]
ports:
- containerPort: 5432
name: dbport
....
volumeMounts:
- mountPath: /scripts
name: postgres-scripts
volumes:
- name: postgres-scripts
configMap:
name: postgres-configmap-initscripts
items:
- key: poststart.sh
path: poststart.sh
The error I am getting:

Answer 1

postStart hook will be call at least once but may be call more than once, this is not a good place to run script.
The poststart.sh file that mounted as ConfigMap will not have execute mode hence the permission error.
It is better to run script in initContainers, here's an quick example that do a simple chmod; while in your case you can execute the script instead:
cat << EOF | kubectl apply -f -
apiVersion: v1
kind: ConfigMap
metadata:
name: busybox
data:
test.sh: |
#!/bin/bash
echo "It's done"
---
apiVersion: v1
kind: Pod
metadata:
name: busybox
labels:
run: busybox
spec:
volumes:
- name: scripts
configMap:
name: busybox
items:
- key: test.sh
path: test.sh
- name: runnable
emptyDir: {}
initContainers:
- name: prepare
image: busybox
imagePullPolicy: IfNotPresent
command: ["ash","-c"]
args: ["cp /scripts/test.sh /runnable/test.sh && chmod +x /runnable/test.sh"]
volumeMounts:
- name: scripts
mountPath: /scripts
- name: runnable
mountPath: /runnable
containers:
- name: busybox
image: busybox
imagePullPolicy: IfNotPresent
command: ["ash","-c"]
args: ["while :; do . /runnable/test.sh; sleep 1; done"]
volumeMounts:
- name: scripts
mountPath: /scripts
- name: runnable
mountPath: /runnable
EOF