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# 一、ReplicaSet控制器简介
## 1.1 ReplicaSet控制器简介
ReplicaSet控制器的主要作用是保证一定数量的pod能能够正常运行，它会持续监听这些pod的运行状态，一旦pod发生故障，就会重启或重建，同时它还支持对pod数量的扩缩容和版本镜像的升级
![](/static/upload/20220523_134308.png)

## 1.2 ReplicaSet控制资源清单文件
```yaml
apiVersion: apps/v1   # 版本号
kind: ReplicaSet    # 类型
metadata:    # 元数据
  name:     # rs名称
  namespace:    # 所属命名空间
  labels:    # 标签
    controller: rs
spec:    # 性情描述
  replicas: 3    # 副本数量
  selector:    # 选择器，通过它指定该控制器管理哪些pod
    matchLabels:    # label匹配规则
      app: nginx-pod
    matchExpressions:   # Expression匹配规则
      - {key: app, operator: In, values: [nginx-pod]}
  template:  # 模板，当副本数量不足时，会根据下面的额模板创建pod副本
    metadata:
      labels:
        app: nginx-pod
    spec:
      containers:
      - name: nginx
        image: nginx:1.17.1
        ports:
        - containerPort:80
 
```
这里面spec中的常用的几个参数含义：
* replicas：指定部分数量，其实就是当前rs创建出来的pod的数量，默认为1
* selector：选择器，它的作用是建立pod控制器和pod之间的关联关系，采用的Label Selector机制，在pod模板上 定义label，在控制器上定义选择器，就可以表明当前控制器能管理哪些pod了
* template：模板，就是当前控制器创建pod所使用的模板，里面其实就是pod的定义

# 二、ReplicaSet实例演示
## 2.1 ReplicaSet控制器创建
编辑replicaset.yaml文件，内容如下：
```yaml
apiVersion: v1
kind: Namespace
metadata:
  name: dev

---

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: pc-replicaset
  namespace: dev
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx-pod
  template:
    metadata:
      labels:
        app: nginx-pod
    spec:
      containers:
      - name: nginx
        image: nginx:1.17.1
```
使用如下命令创建资源
```bash
[root@master pod_controller]# kubectl apply -f replicaset.yaml
namespace/dev created
replicaset.apps/pc-replicaset created
[root@master pod_controller]#
```
通过如下命令可以查询到创建结果
```bash
[root@master pod_controller]# kubectl get rs,pod -n dev -o wide
NAME                            DESIRED   CURRENT   READY   AGE     CONTAINERS   IMAGES         SELECTOR
replicaset.apps/pc-replicaset   3         3         3       2m57s   nginx        nginx:1.17.1   app=nginx-pod

NAME                      READY   STATUS    RESTARTS   AGE     IP            NODE    NOMINATED NODE   READINESS GATES
pod/pc-replicaset-74djl   1/1     Running   0          2m57s   10.244.2.50   node2   <none>           <none>
pod/pc-replicaset-m5tmz   1/1     Running   0          2m57s   10.244.1.23   node1   <none>           <none>
pod/pc-replicaset-wlvcm   1/1     Running   0          2m57s   10.244.1.24   node1   <none>           <none>
[root@master pod_controller]#
```
## 2.2 ReplicaSet实现扩缩容
### 2.2.1 通过修改配置文件方式实现
编辑replicaset.yaml文件，将replicas值设置为6个，如下
```yaml
apiVersion: v1
kind: Namespace
metadata:
  name: dev

---

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: pc-replicaset
  namespace: dev
spec:
  replicas: 6
  selector:
    matchLabels:
      app: nginx-pod
  template:
    metadata:
      labels:
        app: nginx-pod
    spec:
      containers:
      - name: nginx
        image: nginx:1.17.1
```
然后通过如下命令使配置生效
```bash
[root@master pod_controller]# kubectl apply -f replicaset.yaml
namespace/dev unchanged
replicaset.apps/pc-replicaset configured
[root@master pod_controller]#
```
通过如下命令可以查看到配置已经生效
```bash
[root@master pod_controller]# kubectl get rs,pod -n dev
NAME                            DESIRED   CURRENT   READY   AGE
replicaset.apps/pc-replicaset   6         6         6       8m43s

NAME                      READY   STATUS    RESTARTS   AGE
pod/pc-replicaset-2bcwc   1/1     Running   0          39s
pod/pc-replicaset-74djl   1/1     Running   0          8m43s
pod/pc-replicaset-7744x   1/1     Running   0          39s
pod/pc-replicaset-7rqz2   1/1     Running   0          39s
pod/pc-replicaset-m5tmz   1/1     Running   0          8m43s
pod/pc-replicaset-wlvcm   1/1     Running   0          8m43s
[root@master pod_controller]#
```
## 2.2.2 通过命令的方式扩缩容
如下，通过如下命令将pod数量缩小到2个
```bash
[root@master pod_controller]# kubectl scale rs pc-replicaset --replicas=2 -n dev
replicaset.apps/pc-replicaset scaled
[root@master pod_controller]#
```
然后使用如下命令查询，可以发现缩容已经完成
```bash
[root@master pod_controller]# kubectl get rs,pod -n dev
NAME                            DESIRED   CURRENT   READY   AGE
replicaset.apps/pc-replicaset   2         2         2       11m

NAME                      READY   STATUS    RESTARTS   AGE
pod/pc-replicaset-m5tmz   1/1     Running   0          11m
pod/pc-replicaset-wlvcm   1/1     Running   0          11m
[root@master pod_controller]#
```
## 2.3 ReplicaSet实现镜像版本的升降级
## 2.3.1 通过修改配置文件的方式升级镜像版本
编辑yaml文件，修改镜像版本为1.17.3，如下：
```yaml
apiVersion: v1
kind: Namespace
metadata:
  name: dev

---

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: pc-replicaset
  namespace: dev
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx-pod
  template:
    metadata:
      labels:
        app: nginx-pod
    spec:
      containers:
      - name: nginx
        image: nginx:1.17.3
```
然后使用如下命令使配置生效
```bash
[root@master pod_controller]# kubectl apply -f replicaset.yaml
namespace/dev unchanged
replicaset.apps/pc-replicaset configured
[root@master pod_controller]#
```
通过如下命令，可以发现镜像版本已经升级
```bash
[root@master pod_controller]# kubectl get rs,pod -n dev -o wide
NAME                            DESIRED   CURRENT   READY   AGE   CONTAINERS   IMAGES         SELECTOR
replicaset.apps/pc-replicaset   2         2         2       15m   nginx        nginx:1.17.3   app=nginx-pod

NAME                      READY   STATUS    RESTARTS   AGE   IP            NODE    NOMINATED NODE   READINESS GATES
pod/pc-replicaset-m5tmz   1/1     Running   0          15m   10.244.1.23   node1   <none>           <none>
pod/pc-replicaset-wlvcm   1/1     Running   0          15m   10.244.1.24   node1   <none>           <none>
[root@master pod_controller]#
```
### 2.3.2 通过命令的方式对镜像版本升降级
使用如下命令，将镜像版本再降到1.17.1
```bash
[root@master pod_controller]# kubectl set image rs pc-replicaset nginx=nginx:1.17.1 -n dev
replicaset.apps/pc-replicaset image updated
[root@master pod_controller]#
```
通过如下命令查询，可以发现已经生效
```bash
[root@master pod_controller]# kubectl get rs,pod -n dev -o wide
NAME                            DESIRED   CURRENT   READY   AGE   CONTAINERS   IMAGES         SELECTOR
replicaset.apps/pc-replicaset   2         2         2       17m   nginx        nginx:1.17.1   app=nginx-pod

NAME                      READY   STATUS    RESTARTS   AGE   IP            NODE    NOMINATED NODE   READINESS GATES
pod/pc-replicaset-m5tmz   1/1     Running   0          17m   10.244.1.23   node1   <none>           <none>
pod/pc-replicaset-wlvcm   1/1     Running   0          17m   10.244.1.24   node1   <none>           <none>
[root@master pod_controller]#
```
## 2.4 删除ReplicaSet
### 2.4.1 命令行方式删除ReplicaSet以及Pod
使用如下命令删除，在删除ReplicaSet前，会先把pod数量调整为0，等所有pod都删除后，再删除ReplicaSet
```bash
kubectl delete rs pc-replicaset -n dev
```
### 2.4.2 仅删除ReplicaSet，保留Pod
使用如下命令即可
```bash
kubectl delete rs pc-replicaset -n dev --cascade=false
```
### 2.4.3 使用yaml文件删除
使用如下命令（推荐）
```bash
kubectl delete -f replicaset.yaml
```

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