Kubernetes K8S之资源控制器RC、RS、Deployment详解

Kubernetes的资源控制器ReplicationController（RC）、ReplicaSet（RS）、Deployment（Deploy）详解与示例

主机配置规划

服务器名称(hostname)	系统版本	配置	内网IP	外网IP(模拟)
k8s-master	CentOS7.7	2C/4G/20G	172.16.1.110	10.0.0.110
k8s-node01	CentOS7.7	2C/4G/20G	172.16.1.111	10.0.0.111
k8s-node02	CentOS7.7	2C/4G/20G	172.16.1.112	10.0.0.112

什么是控制器

kubernetes中内建了很多controller（控制器），这些相当于一个状态机，用来控制pod的具体状态和行为。

部分控制器类型如下：

• ReplicationController 和 ReplicaSet
• Deployment
• DaemonSet
• StatefulSet
• Job/CronJob
• HorizontalPodAutoscaler

ReplicationController 和 ReplicaSet

ReplicationController (RC)用来确保容器应用的副本数始终保持在用户定义的副本数，即如果有容器异常退出，会自动创建新的pod来替代；而异常多出来的容器也会自动回收。

在新版的Kubernetes中建议使用ReplicaSet (RS)来取代ReplicationController。ReplicaSet跟ReplicationController没有本质的不同，只是名字不一样，但ReplicaSet支持集合式selector。

虽然 ReplicaSets 可以独立使用，但如今它主要被Deployments 用作协调 Pod 的创建、删除和更新的机制。当使用 Deployment 时，你不必担心还要管理它们创建的 ReplicaSet，Deployment 会拥有并管理它们的 ReplicaSet。

ReplicaSet 是下一代的 Replication Controller。 ReplicaSet 和 Replication Controller 的唯一区别是选择器的支持。ReplicaSet 支持新的基于集合的选择器需求，这在标签用户指南中有描述。而 Replication Controller 仅支持基于相等选择器的需求。

Deployments

Deployment 控制器为 Pods和 ReplicaSets提供描述性的更新方式。用来替代以前的ReplicationController以方便管理应用。

典型的应用场景包括：

• 定义Deployment来创建Pod和ReplicaSet
• 滚动升级和回滚应用
• 扩容和缩容
• 暂停和继续Deployment

ReplicaSet示例

yaml文件

[root@k8s-master controller]# pwd
/root/k8s_practice/controller
[root@k8s-master controller]# cat ReplicaSet-01.yaml 
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: frontend
spec:
  replicas: 3
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        tier: frontend
    spec:
      containers:
      - name: nginx
        image: registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17
        imagePullPolicy: IfNotPresent
        ports:
        - name: httpd
          containerPort: 80

创建ReplicaSet，并查看rs状态与详情

[root@k8s-master controller]# kubectl apply -f ReplicaSet-01.yaml 
replicaset.apps/frontend created
[root@k8s-master controller]# kubectl get rs -o wide    # 查看状态
NAME       DESIRED   CURRENT   READY   AGE     CONTAINERS   IMAGES                                                        SELECTOR
frontend   3         3         3       2m12s   nginx        registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17   tier=frontend
[root@k8s-master controller]# 
[root@k8s-master controller]# kubectl describe rs frontend   # 查看详情
Name:         frontend
Namespace:    default
Selector:     tier=frontend
Labels:       
Annotations:  kubectl.kubernetes.io/last-applied-configuration:
                {"apiVersion":"apps/v1","kind":"ReplicaSet","metadata":{"annotations":{},"name":"frontend","namespace":"default"},"spec":{"replicas":3,"se...
Replicas:     3 current / 3 desired
Pods Status:  3 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  tier=frontend
  Containers:
   nginx:
    Image:        registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17
    Port:         80/TCP
    Host Port:    0/TCP
    Environment:  
    Mounts:       
  Volumes:        
Events:
  Type    Reason            Age    From                   Message
  ----    ------            ----   ----                   -------
  Normal  SuccessfulCreate  10m    replicaset-controller  Created pod: frontend-kltwp
  Normal  SuccessfulCreate  10m    replicaset-controller  Created pod: frontend-76dbn
  Normal  SuccessfulCreate  10m    replicaset-controller  Created pod: frontend-jk8td

查看pod状态信息

[root@k8s-master controller]# kubectl get pod -o wide --show-labels
NAME             READY   STATUS    RESTARTS   AGE     IP            NODE         NOMINATED NODE   READINESS GATES   LABELS
frontend-76dbn   1/1     Running   0          5m15s   10.244.4.31   k8s-node01                          tier=frontend
frontend-jk8td   1/1     Running   0          5m15s   10.244.2.35   k8s-node02                          tier=frontend
frontend-kltwp   1/1     Running   0          5m15s   10.244.2.34   k8s-node02                          tier=frontend

删除一个pod，然后再次查看

[root@k8s-master controller]# kubectl delete pod frontend-kltwp
pod "frontend-kltwp" deleted
[root@k8s-master controller]# 
[root@k8s-master controller]# kubectl get pod -o wide --show-labels   # 可见重新创建了一个pod
NAME             READY   STATUS    RESTARTS   AGE     IP            NODE         NOMINATED NODE   READINESS GATES   LABELS
frontend-76dbn   1/1     Running   0          7m27s   10.244.4.31   k8s-node01                          tier=frontend
frontend-jk8td   1/1     Running   0          7m27s   10.244.2.35   k8s-node02                          tier=frontend
frontend-mf79k   1/1     Running   0          16s     10.244.4.32   k8s-node01                          tier=frontend

由上可见，rs又新建了一个pod，保证了pod数总是为3.

Deployment示例

创建 Deployment

yaml文件

[root@k8s-master controller]# pwd
/root/k8s_practice/controller
[root@k8s-master controller]# cat nginx-deployment-1.17.1.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  # 重点关注该字段
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17.1
        ports:
        - containerPort: 80
[root@k8s-master controller]# 
[root@k8s-master controller]# cat nginx-deployment-1.17.5.yaml 
api