k8s学习（6）：init容器

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概念

init容器有如下几个特点：

  • init容器总是运行到成功完成为止
  • 每个init容器都必须在下一个init容器启动之前成功完成
  • 如果Pod的init容器失败，kubernetes会不断重启该pod，直到init容器成功为止。如果Pod对应的restartPolicy为Never，他不会重新启动。

image-20200130124724935

实例

init模板

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apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: busybox
    command: ['sh', '-c', 'echo The app is running! && sleep 3600']
  initContainers:
  - name: init-myservice
    image: busybox
    command: ['sh', '-c', 'until nslookup myservice; do echo waiting for myservice; sleep 2; done;']
  - name: init-mydb
    image: busybox
    command: ['sh', '-c', 'until nslookup mydb; do echo waiting for mydb; sleep2; done']

查看pod创建详情

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# 这时候查看pod状态
kubectl get pod
NAME        READY   STATUS     RESTARTS   AGE
myapp-pod   0/1     Init:0/2   0          3m42s

# 查看pod详情,可以看到创建pod成功，但是并没有继续执行下一步，原因是init容器命令并未执行成功
kubectl describe pod myapp-pod
Name:         myapp-pod
Namespace:    default
Priority:     0
Node:         k8s-node01/192.168.128.141
Start Time:   Thu, 30 Jan 2020 15:51:03 +0800
Labels:       app=myapp
Annotations:  <none>
Status:       Pending
IP:           10.244.1.6
...
中间省略
...
Events:
  Type    Reason     Age   From                 Message
  ----    ------     ----  ----                 -------
  Normal  Scheduled  59s   default-scheduler    Successfully assigned default/myapp-pod to k8s-node01
  Normal  Pulling    57s   kubelet, k8s-node01  Pulling image "busybox"
  Normal  Pulled     45s   kubelet, k8s-node01  Successfully pulled image "busybox"
  Normal  Created    45s   kubelet, k8s-node01  Created container init-myservice
  Normal  Started    44s   kubelet, k8s-node01  Started container init-myservice


# 查看pod日志，可以看到nslookup执行不通过
kubectl log myapp-pod -c  init-myservice
log is DEPRECATED and will be removed in a future version. Use logs instead.
Server:		10.96.0.10
Address:	10.96.0.10:53

** server can't find myservice.default.svc.cluster.local: NXDOMAIN

*** Can't find myservice.svc.cluster.local: No answer
*** Can't find myservice.cluster.local: No answer
*** Can't find myservice.default.svc.cluster.local: No answer
*** Can't find myservice.svc.cluster.local: No answer
*** Can't find myservice.cluster.local: No answer


这时候需要创建一个svc，使得init容器可以nslookup执行成功

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apiVersion: v1
kind: Service
metadata:
  name: myservice
spec:
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376
---
apiVersion: v1
kind: Service
metadata:
  name: mydb
spec:
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9377

特殊说明

image-20200130161407116

image-20200130161726618