Code for Inject an Executable Script into a Container in Kubernetes http://blog.phymata.com/2017/07/29/inject-an-executable-script-into-a-container-in-kubernetes/

deployment-first-crack.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: ghost
  labels:
    role: blog
spec:
  replicas: 1
  template:
    metadata:
      labels:
        role: blog
      annotations:
        pod.beta.kubernetes.io/init-containers: '[
            {
                "name": "init-ghost",
                "image": "alpine:3.6",
                "command": ["sh", "-c", "chmod u+x /scripts/..data/wrapper.sh"],
                "volumeMounts": [{"name": "wrapper", "mountPath": "/scripts"}]
            }
        ]'
    spec:
      containers:
      - name: ghost
        image: ghost:0.11-alpine
        command: ["/scripts/wrapper.sh"]
        ports:
        - name: ghost
          containerPort: 2368
          protocol: TCP
        volumeMounts:
        - name: wrapper
          mountPath: /scripts
      volumes:
      - name: wrapper
        configMap:
          name: wrapper

deployment-without-wrapper.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: ghost
  labels:
    app: ghost
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: ghost
    spec:
      containers:
      - name: ghost
        image: ghost:0.11-alpine
        ports:
        - name: ghost
          containerPort: 2368
          protocol: TCP

deployment.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: ghost
  labels:
    role: blog
spec:
  replicas: 1
  template:
    metadata:
      labels:
        role: blog
    spec:
      containers:
      - name: ghost
        image: ghost:0.11-alpine
        command: ["/scripts/wrapper.sh"]
        ports:
        - name: ghost
          containerPort: 2368
          protocol: TCP
        volumeMounts:
        - name: wrapper
          mountPath: /scripts
      volumes:
      - name: wrapper
        configMap:
          name: wrapper
          defaultMode: 0744

terminal.sh

$ minikube start
Starting local Kubernetes v1.7.0 cluster...
Starting VM...
Getting VM IP address...
Moving files into cluster...
Setting up certs...
Starting cluster components...
Connecting to cluster...
Setting up kubeconfig...
Kubectl is now configured to use the cluster.

$ git clone https://gist.github.com/82c039843663de7e7f1e18bf4debe5fa.git inject-exec-script

$ cd inject-exec-script

$ kubectl create configmap wrapper --from-file=wrapper.sh
configmap "wrapper" created

$ kubectl apply -f deployment.yaml
deployment "ghost" created

$ kubectl get pods
NAME                     READY     STATUS    RESTARTS   AGE
ghost-3057289974-zvqm8   1/1       Running   0          30s

$ kubectl logs ghost-3057289974-zvqm8
Do my special initialization here then run the regular entrypoint
...
Ghost is running in development...
Listening on 0.0.0.0:2368
Url configured as: http://localhost:2368
Ctrl+C to shut down

wrapper.sh

#!/bin/sh

set -euo pipefail

echo "Do my special initialization here then run the regular entrypoint"

exec docker-entrypoint.sh npm start