ReplicaSet属于apps群组v1版本，早期大多数控制器都位于extensions/v1beta1，v1beta2,…

ReplicaSet工作流程

在Controller Manager中有一段代码称为ReplicaSet的控制器代码(Controller loop)。而控制器代码需要真正工作起来需要创建出对应的ReplicaSet Object，ReplicaSet Object是用于向API Server请求管理Pod对象（标签选择器选定的对象），如果存在此标签选择器选定的对象，且足量则无需创建，若没有ReplicaSet会借助于控制循环中的代码向APIserver创建出新的Pod，Pod来自于模板定义。然后由Scheduler调度并绑定至某节点，而后pod由kubelet来负责运行。

ReplicaSet资源定义规范

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apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: …
  namespace: …
spec:
  minReadySeconds <integer>  # Pod就绪后多少秒内，Pod任一容器无crash方可视为“就绪”
  replicas <integer> # 期望的Pod副本数，默认为1
  selector: # 标签选择器，必须匹配template字段中Pod模板中的标签；
    matchExpressions <[]Object> # 标签选择器表达式列表，多个列表项之间为“与”关系
    matchLabels <map[string]string> # map格式的标签选择器
  template:  # Pod模板对象
    metadata:  # Pod对象元数据
      labels:  # 由模板创建出的Pod对象所拥有的标签，必须要能够匹配前面定义的标签选择器
    spec:  # Pod规范，格式同自主式Pod
      ……

ReplicaSet示例

1.编写资源清单

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root@k8s-master01:~/yaml/chapter08# vim replicaset-demo.yaml
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: replicaset-demo
spec:
  minReadySeconds: 3
  replicas: 2
  selector:
    matchLabels:
      app: demoapp
      release: stable
      version: v1.0
  template:
    metadata:
      labels:
        app: demoapp
        release: stable
        version: v1.0
    spec:
      containers:
      - name: demoapp
        image: ikubernetes/demoapp:v1.0
        ports:
        - name: http
          containerPort: 80
        livenessProbe:
          httpGet:
            path: '/livez'
            port: 80
          initialDelaySeconds: 5
        readinessProbe:
          httpGet:
            path: '/readyz'
            port: 80
          initialDelaySeconds: 15

2.应用配置清单

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root@k8s-master01:~/yaml/chapter08# kubectl apply -f replicaset-demo.yaml
replicaset.apps/replicaset-demo created

root@k8s-master01:~/yaml/chapter08# kubectl get rs
NAME              DESIRED   CURRENT   READY   AGE
replicaset-demo   2         2         2       15m

3.查看rs的详细信息

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root@k8s-master01:~/yaml/chapter08# kubectl describe rs replicaset-demo
Name:         replicaset-demo
Namespace:    default
Selector:     app=demoapp,release=stable,version=v1.0
Labels:       <none>
Annotations:  <none>
Replicas:     2 current / 2 desired
Pods Status:  2 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=demoapp
           release=stable
           version=v1.0
  Containers:
   demoapp:
    Image:        ikubernetes/demoapp:v1.0
    Port:         80/TCP
    Host Port:    0/TCP
    Liveness:     http-get http://:80/livez delay=5s timeout=1s period=10s #success=1 #failure=3
    Readiness:    http-get http://:80/readyz delay=15s timeout=1s period=10s #success=1 #failure=3
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age   From                   Message
  ----    ------            ----  ----                   -------
  Normal  SuccessfulCreate  89s   replicaset-controller  Created pod: replicaset-demo-62bxh
  Normal  SuccessfulCreate  89s   replicaset-controller  Created pod: replicaset-demo-kwl4r

# rs创建了2个pod

4.查看pod

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root@k8s-master01:~/yaml/chapter08# kubectl get pods
NAME                        READY   STATUS      RESTARTS   AGE
replicaset-demo-62bxh       1/1     Running     0          2m34s
replicaset-demo-kwl4r       1/1     Running     0          2m34s

5.删除pod

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root@k8s-master01:~/yaml/chapter08# kubectl delete pods replicaset-demo-62bxh
pod "replicaset-demo-62bxh" deleted

# 一旦pod被删除，控制器会重新生成一个pod
root@k8s-master01:~/yaml/chapter08# kubectl get pods
NAME                        READY   STATUS      RESTARTS   AGE
replicaset-demo-k2jnl       0/1     Running     0          51s
replicaset-demo-kwl4r       1/1     Running     0          18m

6.导出pod的yaml信息

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root@k8s-master01:~# kubectl get pods replicaset-demo-k2jnl -o yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: "2021-07-21T06:46:44Z"
  generateName: replicaset-demo-
  labels:
    app: demoapp
    release: stable
    version: v1.0
  name: replicaset-demo-k2jnl
  namespace: default
  ownerReferences:                        # 此处可以看到Pod归谁所有。
  - apiVersion: apps/v1
    blockOwnerDeletion: true
    controller: true
    kind: ReplicaSet
    name: replicaset-demo
    uid: d16ab83c-c9a6-486f-b202-72e93f982750
  resourceVersion: "1196532"
  uid: b7478159-6cbd-4139-8954-7758e46679c3

ReplicaSet应用的更新和回滚

ReplicaSet更新机制

ReplicaSet支持两种更新

  • 删除式更新：在修改时只修改了APIServer中的pod模板信息，而ReplicaSet标签选择器所选定的pod数量足够时，其不会立即更新，需要删除当前的Pod后才会使用新的模板创建出pod.
  • 单批次删除所有Pod，一次完成所有更新；服务会中断一段时间；
  • 分批次删除，待一批次就绪之后，才删除下一批；滚动更新；
删除式更新示例

1.查看ReplicaSet信息

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root@k8s-master01:~# kubectl get rs -o wide
NAME              DESIRED   CURRENT   READY   AGE   CONTAINERS   IMAGES                     SELECTOR
replicaset-demo   2         2         2       41m   demoapp      ikubernetes/demoapp:v1.0   app=demoapp,release=stable,version=v1.0

2.现在将demoapp:v1.0升级到demoapp:v1.1

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# 命令式更新使用kubectl Set来进行设定
root@k8s-master01:~# kubectl set image replicasets/replicaset-demo demoapp=ikubernetes/demoapp:v1.1  
replicaset.apps/replicaset-demo image updated

# 查看pod
root@k8s-master01:~# kubectl get pods -l 'app=demoapp' -o wide
NAME                      READY   STATUS      RESTARTS   AGE   IP            NODE         NOMINATED NODE   READINESS GATES
replicaset-demo-k2jnl     1/1     Running     3          29m   10.244.2.24   k8s-node02   <none>           <none>
replicaset-demo-kwl4r     1/1     Running     0          46m   10.244.3.27   k8s-node03   <none>           <none>

# 查看pod是否被跟新
root@k8s-master01:~# curl 10.244.3.27
iKubernetes demoapp v1.0 !! ClientIP: 10.244.0.0, ServerName: replicaset-demo-kwl4r, ServerIP: 10.244.3.27!
# 目前依旧未被跟新，主要是因为使用命令方式更新为删除式更新，需要将pod删除后才会进行更新

3.删除pod，并再次查看

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root@k8s-master01:~# kubectl delete pods replicaset-demo-kwl4r
pod "replicaset-demo-kwl4r" deleted

# 再次查看
root@k8s-master01:~# kubectl get pods -l 'app=demoapp' -o wide
NAME                      READY   STATUS      RESTARTS   AGE   IP            NODE         NOMINATED NODE   READINESS GATES
replicaset-demo-5fmvs     0/1     Running     0          44s   10.244.3.28   k8s-node03   <none>           <none>    # 此为新创建的pod
replicaset-demo-k2jnl     1/1     Running     3          40m   10.244.2.24   k8s-node02   <none>           <none>

4.访问新创建出的Pod

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root@k8s-master01:~# curl 10.244.3.28
iKubernetes demoapp v1.1 !! ClientIP: 10.244.0.0, ServerName: replicaset-demo-5fmvs, ServerIP: 10.244.3.28!
# pod已经被更新