init container

init container与应用容器在本质上是一样的, 但它们是仅运行一次就结束的任务, 并且必须在成功执行完成后, 系统才能继续执行下一个容器， 可以用在例如应用容器启动前做一些初始化工作，当init container执行失败, 而且设置了RestartPolicy=Never时, Pod将会启动失败, 而设置了RestartPolicy=Always时, pod将会被系统自动重启

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  namespace: default
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx
    spec:
      initContainers:
      - name: install
        image: busybox
        imagePullPolicy: IfNotPresent
        command:
        - wget
        - "-O"
        - "/work-dir/index.html"
        - http://kubernetes.io
        volumeMounts:
        - name: workdir
          mountPath: "/work-dir"
      containers:
      - name: nginx
        image: nginx:1.12
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 80
        volumeMounts:
        - name: workdir
          mountPath: "/usr/share/nginx/html"
      volumes:
      - name: workdir
        emptyDir: {} 

---
apiVersion: v1
kind: Service
metadata:
  name: nginx-service
  namespace: default
  labels:
    app: nginx
spec:
  type: NodePort
  selector:
    app: nginx
  ports:
  - name: http
    port: 80
    protocol: TCP
    targetPort: 80
---