Kubernetes - ReplicationController

ReplicationController

정의

• 요구하는 Pod의 개수를 보장하며 파드 집합의 실행을 항상 안정적으로 유지하는 것을 목표
• 요구하는 Pod의 개수가 부족하면 template 이용해 Pod를 추가
• 요구하는 Pod 수 보다 많으면 최근에 생성된 Pod를 삭제
• 기본 구조
• selector
• replicas
• template

실행방법

생성

replicas를 3으로 설정하고 3개의 pod를 생성

root@master:~# cat > rc-nginx.yaml
apiVersion: v1
kind: ReplicationController
metadata:
  name: rc-nginx
spec:
  replicas: 3
  selector:
    app: webui
  template:
    metadata:
      name: nginx-pod
      labels:
        app: webui
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.14
root@master:~# kubectl get pods -o wide
No resources found in default namespace.
root@master:~# kubectl create -f rc-nginx.yaml 
replicationcontroller/rc-nginx created
root@master:~# kubectl get pods -o wide
NAME             READY   STATUS              RESTARTS   AGE   IP       NODE                NOMINATED NODE   READINESS GATES
rc-nginx-cdlxb   0/1     ContainerCreating   0          3s    <none>   node1.example.com   <none>           <none>
rc-nginx-cgsgj   0/1     ContainerCreating   0          3s    <none>   node1.example.com   <none>           <none>
rc-nginx-v5mbf   0/1     ContainerCreating   0          3s    <none>   node2.example.com   <none>           <none>

조회

root@master:~# kubectl get rc -o wide
NAME       DESIRED   CURRENT   READY   AGE     CONTAINERS        IMAGES       SELECTOR
rc-nginx   3         3         3       3m52s   nginx-container   nginx:1.14   app=webui

replicas 개수 수정 (edit 명령어)

3개에서 2개로 수정하고 나서 조회해보자

root@master:~# kubectl edit rc rc-nginx

########################################################################################
# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: v1
kind: ReplicationController
metadata:
  creationTimestamp: "2021-11-19T11:50:11Z"
  generation: 1
  labels:
    app: webui
  name: rc-nginx
  namespace: default
  resourceVersion: "75124"
  uid: 6f7dcbd8-9a8f-435a-a1fa-3f9308a6f55d
spec:
  replicas: 2
  selector:
    app: webui
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: webui
      name: nginx-pod
    spec:
      containers:
      - image: nginx:1.14
        imagePullPolicy: IfNotPresent
        name: nginx-container
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      terminationGracePeriodSeconds: 30
status:
  availableReplicas: 3
  fullyLabeledReplicas: 3
  observedGeneration: 1
  readyReplicas: 3
  replicas: 3
########################################################################################

root@master:~# kubectl get pods -o wide
NAME             READY   STATUS    RESTARTS   AGE     IP          NODE                NOMINATED NODE   READINESS GATES
rc-nginx-cgsgj   1/1     Running   0          5m26s   10.36.0.1   node1.example.com   <none>           <none>
rc-nginx-v5mbf   1/1     Running   0          5m26s   10.44.0.1   node2.example.com   <none>           <none>
root@master:~# kubectl get rc -o wide
NAME       DESIRED   CURRENT   READY   AGE     CONTAINERS        IMAGES       SELECTOR
rc-nginx   2         2         2       5m29s   nginx-container   nginx:1.14   app=webui

 

replicas 개수 수정 (scale 명령어)

root@master:~# kubectl scale rc rc-nginx --replicas=5
replicationcontroller/rc-nginx scaled
root@master:~# kubectl get rc -o wide
NAME       DESIRED   CURRENT   READY   AGE     CONTAINERS        IMAGES       SELECTOR
rc-nginx   5         5         5       6m43s   nginx-container   nginx:1.14   app=webui
root@master:~# kubectl get pods -o wide
NAME             READY   STATUS    RESTARTS   AGE     IP          NODE                NOMINATED NODE   READINESS GATES
rc-nginx-8wnzt   1/1     Running   0          8s      10.44.0.2   node2.example.com   <none>           <none>
rc-nginx-cgsgj   1/1     Running   0          6m46s   10.36.0.1   node1.example.com   <none>           <none>
rc-nginx-h2n5l   1/1     Running   0          8s      10.44.0.3   node2.example.com   <none>           <none>
rc-nginx-ps97l   1/1     Running   0          8s      10.36.0.2   node1.example.com   <none>           <none>
rc-nginx-v5mbf   1/1     Running   0          6m46s   10.44.0.1   node2.example.com   <none>           <none>

파드 개수 보장 확인

생성된 rc-nginx에서 임의의 pod 한개를 삭제하였을 때 설정된 개수만큼 다시 재생성되는지 확인

root@master:~# kubectl get pods -o wide
NAME             READY   STATUS    RESTARTS   AGE     IP          NODE                NOMINATED NODE   READINESS GATES
rc-nginx-8wnzt   1/1     Running   0          37s     10.44.0.2   node2.example.com   <none>           <none>
rc-nginx-cgsgj   1/1     Running   0          7m15s   10.36.0.1   node1.example.com   <none>           <none>
rc-nginx-h2n5l   1/1     Running   0          37s     10.44.0.3   node2.example.com   <none>           <none>
rc-nginx-ps97l   1/1     Running   0          37s     10.36.0.2   node1.example.com   <none>           <none>
rc-nginx-v5mbf   1/1     Running   0          7m15s   10.44.0.1   node2.example.com   <none>           <none>
root@master:~# kubectl get replicationcontrollers
NAME       DESIRED   CURRENT   READY   AGE
rc-nginx   5         5         5       7m39s
root@master:~# kubectl delete pod rc-nginx-v5mbf
pod "rc-nginx-v5mbf" deleted
root@master:~# kubectl get pods -o wide
NAME             READY   STATUS    RESTARTS   AGE     IP          NODE                NOMINATED NODE   READINESS GATES
rc-nginx-8wnzt   1/1     Running   0          2m26s   10.44.0.2   node2.example.com   <none>           <none>
rc-nginx-9p8jc   1/1     Running   0          5s      10.36.0.3   node1.example.com   <none>           <none>
rc-nginx-cgsgj   1/1     Running   0          9m4s    10.36.0.1   node1.example.com   <none>           <none>
rc-nginx-h2n5l   1/1     Running   0          2m26s   10.44.0.3   node2.example.com   <none>           <none>
rc-nginx-ps97l   1/1     Running   0          2m26s   10.36.0.2   node1.example.com   <none>           <none>

rc-nginx-v5mbf 라는 임의의 파드를 삭제하였지만 다시 rc-nginx-9p8jc 라는 파드가 재생성되었음을 확인할 수 있다.