InitContainer用途：

1、Init 容器可以包含一些安装过程中应用容器中不存在的实用工具或个性化代码；
2、Init 容器可以安全地运行这些工具，避免这些工具导致应用镜像的安全性降低；
3、Init容器可以以root身份运行，执行一些高权限命令；
4、Init容器相关操作执行完成以后即退出，不会给业务容器带来安全隐患。

初始化容器和PostStart区别

PostStart：依赖主应用的环境，而且并不一定先于Command运行。
InitContainer：不依赖主应用的环境，可以有更高的权限和更多的工具，一定会在主应用启动之前完成。

初始化容器和普通容器的区别

1、它们总是运行到完成；
2、上一个运行完成才会运行下一个；
3、如果 Pod 的 Init 容器失败，Kubernetes 会不断地重启该 Pod，直到 Init 容器成功为止，但是Pod 对应的 restartPolicy 值为 Never，Kubernetes 不会重新启动 Pod。
4、Init 容器不支持 lifecycle、livenessProbe、readinessProbe 和 startupProbe。

示例：

注意：init容器修改或生成的配置，必须用volume挂载到容器中

示例1：

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: es-cluster
spec:
  serviceName: elasticsearch
  replicas: 3
  selector:
    matchLabels:
      app: elasticsearch
  template:
    metadata:
      labels:
        app: elasticsearch
    spec:
      volumes:
      - name: data
        emptyDir: {}
      initContainers:
      - name: fix-permissions
        image: busybox
        command: ["sh", "-c", "chown -R 1000:1000 /usr/share/elasticsearch/data"]
        securityContext:
          privileged: true
        volumeMounts:
        - name: data
          mountPath: /usr/share/elasticsearch/data
      - name: increase-vm-max-map
        image: busybox
        command: ["sysctl", "-w", "vm.max_map_count=262144"]
        securityContext:
          privileged: true
      - name: increase-fd-ulimit
        image: busybox
        command: ["sh", "-c", "ulimit -n 65536"]
        securityContext:
          privileged: true
      containers:
      - name: elasticsearch
        #image: docker.elastic.co/elasticsearch/elasticsearch-oss:6.4.3
        image: dotbalo/es:2.4.6-cluster
        imagePullPolicy: Always
        resources:
            limits:
              cpu: 1000m
            requests:
              cpu: 100m
        ports:
        - containerPort: 9200
          name: rest
          protocol: TCP
        - containerPort: 9300
          name: inter-node
          protocol: TCP
        volumeMounts:
        - name: data
          mountPath: /usr/share/elasticsearch/data
        env:
          - name: "cluster.name"
            value: "pscm-cluster"
          - name: "CLUSTER_NAME"
            value: "pscm-cluster"
          - name: "discovery.zen.minimum_master_nodes"
            value: "2"
          - name: "MINIMUM_MASTER_NODES"
            value: "2"
          - name: "node.name"
            valueFrom:
              fieldRef:
                fieldPath: metadata.name
          - name: "NODE_NAME"
            valueFrom:
              fieldRef:
                fieldPath: metadata.name
          - name: "discovery.zen.ping.unicast.hosts"
            value: "es-cluster-0.elasticsearch, es-cluster-1.elasticsearch, es-cluster-2.elasticsearch"
          #- name: ES_JAVA_OPTS
          #  value: "-Xms512m -Xmx512m"

示例2：

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: test-init
  name: test-init
  namespace: kube-public
spec:
  replicas: 1
  selector:
    matchLabels:
      app: test-init
  template:
    metadata:
      labels:
        app: test-init
    spec:
      volumes:
      - name: data
        emptyDir: {}
      initContainers:
      - command:
        - sh
        - -c
        - touch /mnt/test-init.txt
        image: nginx
        imagePullPolicy: IfNotPresent
        name: init-touch
        volumeMounts:
        - name: data
          mountPath: /mnt
      containers:
      - image: nginx
        imagePullPolicy: IfNotPresent
        name: test-init
        volumeMounts:
        - name: data
          mountPath: /mnt

示例3：

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: test-init
  name: test-init
  namespace: kube-public
spec:
  replicas: 3
  selector:
    matchLabels:
      app: test-init
  template:
    metadata:
      labels:
        app: test-init
    spec:
      volumes:
      - name: data
        emptyDir: {}
      initContainers:
      - command:
        - sh
        - -c
        - touch /mnt/test-init.txt
        image: nginx
        imagePullPolicy: IfNotPresent
        name: init-touch
        volumeMounts:
        - name: data
          mountPath: /mnt
      - command:
        - sh
        - -c
        - for i in `seq 1 100`; do echo $i; sleep 1; done
        image: nginx
        imagePullPolicy: IfNotPresent
        name: echo
      containers:
      - image: nginx
        imagePullPolicy: IfNotPresent
        name: test-init
        volumeMounts:
        - name: data
          mountPath: /mnt