[Kubernetes]Pod: Init container를 적용한 Pod

Init Container

Main container의 전처리를 수행하는 Container

• Init container 수행에 실패하면 Main container는 수행되지 않는 구조

Example

Kubernetes: Init Containers

1. myapp-pod: init-container-exam.yaml 작성
   • myservice라는 앱과 mydb라는 앱이 생성되면 Main container인 myapp-container를 수행

     # init-container-exam.yaml
     apiVersion: v1
     kind: Pod
     metadata:
     name: myapp-pod
     labels:
      app.kubernetes.io/name: MyApp
     spec:
     containers:
            - name: myapp-container
      image: busybox:1.28
      command: ['sh', '-c', 'echo The app is running! && sleep 3600']
     initContainers:
            - name: init-myservice
      image: busybox:1.28
      command: ['sh', '-c', "until nslookup myservice.$(cat /var/run/secrets/kubernetes.io/serviceaccount/namespace).svc.cluster.local; do echo waiting for myservice; sleep 2; done"]
            - name: init-mydb
      image: busybox:1.28
      command: ['sh', '-c', "until nslookup mydb.$(cat /var/run/secrets/kubernetes.io/serviceaccount/namespace).svc.cluster.local; do echo waiting for mydb; sleep 2; done"]
     

2. myapp-pod 생성
   • init 2개 대기 확인

     master@k8s-master:~/kubernetes/yaml$ kubectl get pods
     NAME        READY   STATUS     RESTARTS   AGE
     myapp-pod   0/1     Init:0/2   0          15s
     

3. Init containers를 생성 시킬 트리거 yaml 작성

   # myservice.yaml
   apiVersion: v1
   kind: Service
   metadata:
     name: myservice
   spec:
     ports:
     - protocol: TCP
    port: 80
    targetPort: 9376
   

   # mydb.yaml
   apiVersion: v1
   kind: Service
   metadata:
     name: mydb
   spec:
     ports:
     - protocol: TCP
    port: 80
    targetPort: 9377
   

4. myservice, mydb를 순서대로 실행하면서 Status 식별

master@k8s-master:~/kubernetes/yaml$ kubectl create -f mydb.yaml
service/mydb created

master@k8s-master:~/kubernetes/yaml$ kubectl get services
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP   47h
mydb         ClusterIP   10.97.155.161   <none>        80/TCP    5s
myservice    ClusterIP   10.110.61.55    <none>        80/TCP    3m39s

master@k8s-master:~/kubernetes/yaml$ kubectl get pods
NAME        READY   STATUS    RESTARTS   AGE
myapp-pod   1/1     Running   0          25m

master@k8s-master:~/kubernetes/yaml$ kubectl create -f myservice.yaml
service/myservice created

master@k8s-master:~/kubernetes/yaml$ kubectl get services
NAME         TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1      <none>        443/TCP   47h
myservice    ClusterIP   10.110.61.55   <none>        80/TCP    35s

master@k8s-master:~/kubernetes/yaml$ kubectl get pods
NAME        READY   STATUS     RESTARTS   AGE
myapp-pod   0/1     Init:1/2   0          20m