# ReplicationController和ReplicaSet ReplicationController用來確保容器應用的副本數始終保持在用戶定義的副本數，即如果有容器異常退出，會自動創建新的Pod來替代；而如果異常多出來的容器也會自動回收。 在新版本的Kubernetes中建議使用ReplicaSet來取代ReplicationController。ReplicaSet跟ReplicationController沒有本質的不同，只是名字不一樣，并且ReplicaSet支持集合式的selector。 雖然ReplicaSet可以獨立使用，但一般還是建議使用 Deployment 來自動管理ReplicaSet，這樣就無需擔心跟其他機制的不兼容問題（比如ReplicaSet不支持rolling-update但Deployment支持）。 ReplicaSet示例： ```yaml apiVersion: extensions/v1beta1 kind: ReplicaSet metadata: name: frontend # these labels can be applied automatically # from the labels in the pod template if not set # labels: # app: guestbook # tier: frontend spec: # this replicas value is default # modify it according to your case replicas: 3 # selector can be applied automatically # from the labels in the pod template if not set, # but we are specifying the selector here to # demonstrate its usage. selector: matchLabels: tier: frontend matchExpressions: - {key: tier, operator: In, values: [frontend]} template: metadata: labels: app: guestbook tier: frontend spec: containers: - name: php-redis image: gcr.io/google_samples/gb-frontend:v3 resources: requests: cpu: 100m memory: 100Mi env: - name: GET_HOSTS_FROM value: dns # If your cluster config does not include a dns service, then to # instead access environment variables to find service host # info, comment out the 'value: dns' line above, and uncomment the # line below. # value: env ports: - containerPort: 80 ```