[K8S] ReplicationController

Controller란?
Pod 의 개수를 보장

Replication Controller (가장 BASIC한 Controller)

• 요구하는 Pod의 개수를 보장하며 파드 집합의 실행을 항상 안정적으로 유지하는 것을 목표
  • 요구하는 Pod의 개수가 부족하면 template을 이용해 Pod cnrk
  • 요구하는 Pod 수보다 많으면 최근에 생성된 Pod 삭제
• 기본 구성 : selector를 replicas 갯수만큼 만들려고 보장해준다
  • selector
  • replicas
  • template
• 구식의 기술로 최근에는 Replica Set으로 대체되고 있다.

 # 실습

[master ~]$ cat > rc-nginx.yaml 
apiVersion: v1
kind: ReplicationController
metadata:   # ReplicationController의 metadata
  name: rc-nginx # 컨테이너 이름
spec:
  replicas: 3
  selector:
    app: webui
  template:
    metadata:    # pod의 metadata
      name: nginx-pod
      labels:
        app: webui
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.14

[master ~]$ kubectl create -f rc-nginx.yaml 
replicationcontroller/rc-nginx created

[master ~]$ kubectl get pods -o wide
NAME             READY   STATUS    RESTARTS   AGE   IP         NODE    NOMINATED NODE   READINESS GATES
rc-nginx-4zzw6   1/1     Running   0          14s   10.5.1.4   node2   <none>           <none>
rc-nginx-qkdvx   1/1     Running   0          14s   10.5.1.5   node2   <none>           <none>
rc-nginx-rn4dp   1/1     Running   0          14s   10.5.1.3   node2   <none>           <none>
# 해시값으로 random한 이름의 Pod가 생성된다.

# RC 확인
[master ~]$ kubectl get replicationcontrollers
NAME       DESIRED   CURRENT   READY   AGE
rc-nginx   3         3         3       4m32s
[master ~]$ kubectl get rc
NAME       DESIRED   CURRENT   READY   AGE
rc-nginx   3         3         3       12m

# 좀 더 자세히 확인
[master ~]$ kubectl describe rc rc-nginx 
Name:         rc-nginx
Namespace:    default
Selector:     app=webui
Labels:       app=webui
Annotations:  <none>
Replicas:     3 current / 3 desired
Pods Status:  3 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=webui
  Containers:
   nginx-container:
    Image:        nginx:1.14
    Port:         <none>
    Host Port:    <none>
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age   From                    Message
  ----    ------            ----  ----                    -------
  Normal  SuccessfulCreate  12m   replication-controller  Created pod: rc-nginx-rn4dp
  Normal  SuccessfulCreate  12m   replication-controller  Created pod: rc-nginx-4zzw6
  Normal  SuccessfulCreate  12m   replication-controller  Created pod: rc-nginx-qkdvx

 

# Yaml 로 만들어보기

[master ~]$ kubectl run redis --image=redis --labels=app=webui --dry-run
W0219 08:38:04.821497   17456 helpers.go:692] --dry-run is deprecated and can be replaced with --dry-run=client.
pod/redis created (dry run)
[master ~]$ kubectl run redis --image=redis --labels=app=webui --dry-run -o yaml > redis.yaml
W0219 08:40:17.236640   17703 helpers.go:692] --dry-run is deprecated and can be replaced with --dry-run=client.


[master ~]$ cat redis.yaml 
apiVersion: v1
kind: Pod
metadata:
  labels: # 단지 여기만 추가되는 것!
    app: webui
  name: redis
spec:
  containers:
  - image: redis
    name: redis

[master ~]$ kubectl get pod --show-labels
NAME             READY   STATUS    RESTARTS   AGE   LABELS
rc-nginx-4zzw6   1/1     Running   0          27m   app=webui
rc-nginx-qkdvx   1/1     Running   0          27m   app=webui
rc-nginx-rn4dp   1/1     Running   0          27m   app=webui

 

# Scale-out

- Kubenetes는 Horizontal Scale-out을 해준다.

[master ~]$ kubectl edit rc rc-nginx 
replicationcontroller/rc-nginx edited

[master ~]$ kubectl get pod --show-labels
NAME             READY   STATUS    RESTARTS   AGE   LABELS
rc-nginx-4zzw6   1/1     Running   0          65m   app=webui
rc-nginx-qkdvx   1/1     Running   0          65m   app=webui
rc-nginx-rn4dp   1/1     Running   0          65m   app=webui
rc-nginx-svjqk   1/1     Running   0          4s    app=webui

 

kubectl edit을 통한 scale-out

밑에 Template 영역은 Pod Template이다. 

👉image: nginx:1.15 로 바꿔주면 변화가 있는 가? No!
Controller는 selector만 본다. 이미 app=webui가 이미 2개가 동작중이기 때문에 아무런 영향이 없다.

nginx 1.14버전으로 동작중임

 

# 삭제하고 다시 확인해보기
[master ~]$ kubectl delete pod rc-nginx-4zzw6 
pod "rc-nginx-4zzw6" deleted

[master ~]$ kubectl get pod --show-labels
NAME             READY   STATUS    RESTARTS   AGE   LABELS
rc-nginx-qkdvx   1/1     Running   0          75m   app=webui
rc-nginx-svwxv   1/1     Running   0          12s   app=webui
[master ~]$ kubectl describe pod rc-nginx-svwxv 
Name:             rc-nginx-svwxv
Namespace:        default
Priority:         0
Service Account:  default
Node:             node2/192.168.0.12
Start Time:       Mon, 19 Feb 2024 09:38:07 +0000
Labels:           app=webui
Annotations:      <none>
Status:           Running
IP:               10.5.1.7
IPs:
  IP:           10.5.1.7
Controlled By:  ReplicationController/rc-nginx
Containers:
  nginx-container:
    Container ID:   containerd://abf400960952b3251d7645d9c81ea0310e130719f62ef17ac345b31381cd7a78
    Image:          nginx:1.15 # 1.15버전 된 것 확인가능
    Image ID:       docker.io/library/nginx@sha256:23b4dcdf0d34d4a129755fc6f52e1c6e23bb34ea011b315d87e193033bcd1b68
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Mon, 19 Feb 2024 09:38:13 +0000
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-rt4ng (ro)
      
 # 서비스 동작 중에 1.14 -> 1.15 버전으로 바뀌었다 = 롤링 업데이트 (비즈니스 연속성)

 

# 명령어로 scale-down

[master ~]$ kubectl scale rc rc-nginx --replicas=2
replicationcontroller/rc-nginx scaled

[master ~]$ kubectl get pod --show-labels
NAME             READY   STATUS    RESTARTS   AGE   LABELS
rc-nginx-4zzw6   1/1     Running   0          68m   app=webui
rc-nginx-qkdvx   1/1     Running   0          68m   app=webui