InitContainer用途：

1帮辟、Init 容器可以包含一些安裝過(guò)程中應(yīng)用容器中不存在的實(shí)用工具或個(gè)性化代碼旭绒；
2、Init 容器可以安全地運(yùn)行這些工具首昔，避免這些工具導(dǎo)致應(yīng)用鏡像的安全性降低；
3糙俗、Init容器可以以root身份運(yùn)行勒奇，執(zhí)行一些高權(quán)限命令；
4巧骚、Init容器相關(guān)操作執(zhí)行完成以后即退出赊颠，不會(huì)給業(yè)務(wù)容器帶來(lái)安全隱患。

初始化容器和PostStart區(qū)別

PostStart：依賴主應(yīng)用的環(huán)境劈彪，而且并不一定先于Command運(yùn)行竣蹦。
InitContainer：不依賴主應(yīng)用的環(huán)境，可以有更高的權(quán)限和更多的工具沧奴，一定會(huì)在主應(yīng)用啟動(dòng)之前完成痘括。

初始化容器和普通容器的區(qū)別

1、它們總是運(yùn)行到完成滔吠；
2纲菌、上一個(gè)運(yùn)行完成才會(huì)運(yùn)行下一個(gè)；
3疮绷、如果 Pod 的 Init 容器失敗翰舌，Kubernetes 會(huì)不斷地重啟該 Pod，直到 Init 容器成功為止冬骚，但是Pod 對(duì)應(yīng)的 restartPolicy 值為 Never椅贱，Kubernetes 不會(huì)重新啟動(dòng) Pod。
4只冻、Init 容器不支持 lifecycle庇麦、livenessProbe、readinessProbe 和 startupProbe喜德。

示例：

注意：init容器修改或生成的配置山橄，必須用volume掛載到容器中

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