Kubernetes中文文档

名词解释:ReplicaSets

什么是ReplicaSet?

ReplicaSet是下一代复本控制器。ReplicaSet和 Replication Controller之间的唯一区别是现在的选择器支持。Replication Controller只支持基于等式的selector(env=dev或environment!=qa),但ReplicaSet还支持新的,基于集合的selector(version in (v1.0, v2.0)或env notin (dev, qa))。在试用时官方推荐ReplicaSet。

大多数kubectl支持Replication Controller的命令也支持ReplicaSets。rolling-update命令有一个例外 。如果您想要滚动更新功能,请考虑使用Deployments。此外, rolling-update命令是必须的,而Deployments是声明式的,因此我们建议通过rollout命令使用Deployments。

虽然ReplicaSets可以独立使用,但是今天它主要被 Deployments 作为协调pod创建,删除和更新的机制。当您使用Deployments时,您不必担心管理他们创建的ReplicaSets。Deployments拥有并管理其ReplicaSets。

何时使用ReplicaSet?

ReplicaSet可确保指定数量的pod“replicas”在任何设定的时间运行。然而,Deployments是一个更高层次的概念,它管理ReplicaSets,并提供对pod的声明性更新以及许多其他的功能。因此,我们建议您使用Deployments而不是直接使用ReplicaSets,除非您需要自定义更新编排或根本不需要更新。

这实际上意味着您可能永远不需要操作ReplicaSet对象:直接使用Deployments并在规范部分定义应用程序。

frontend.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

将此配置保存frontend.yaml到Kubernetes集群并将其提交给Kubernetes集群时,应创建定义的ReplicaSet及其管理的pod。

$ kubectl create -f frontend.yaml
replicaset "frontend" created
$ kubectl describe rs/frontend
Name:          frontend
Namespace:     default
Image(s):      gcr.io/google_samples/gb-frontend:v3
Selector:      tier=frontend,tier in (frontend)
Labels:        app=guestbook,tier=frontend
Replicas:      3 current / 3 desired
Pods Status:   3 Running / 0 Waiting / 0 Succeeded / 0 Failed
No volumes.
Events:
  FirstSeen    LastSeen    Count    From                SubobjectPath    Type        Reason            Message
  ---------    --------    -----    ----                -------------    --------    ------            -------
  1m           1m          1        {replicaset-controller }             Normal      SuccessfulCreate  Created pod: frontend-qhloh
  1m           1m          1        {replicaset-controller }             Normal      SuccessfulCreate  Created pod: frontend-dnjpy
  1m           1m          1        {replicaset-controller }             Normal      SuccessfulCreate  Created pod: frontend-9si5l
$ kubectl get pods
NAME             READY     STATUS    RESTARTS   AGE
frontend-9si5l   1/1       Running   0          1m
frontend-dnjpy   1/1       Running   0          1m
frontend-qhloh   1/1       Running   0          1m