Kubernetes基础：RC(Replication Controller) vs RS(Replica Set)的使用方式

叁歲伎倆 2023-07-03 10:51 29阅读 0赞

RC(Replication Controller)是早期Kubernetes版本提供的Pod，在现在版本中已经被建议使用Replica Set所代替（准确地说是使用Deployment配合ReplicaSet进行替代），这篇文章就二者的区别以使用方式进行介绍。

# 使用示例: RC #

首先我们通过一个简单的示例来看一下RC的使用方式。YAML设定文件如下所示：

[root@host131 ReplicaSet]# cat busybox-rc.yaml 
    ---
    apiVersion: v1
    kind: ReplicationController
    metadata:
      name: test-rc
    spec:
      replicas: 1
      selector:
        app: busybox-pod
      template:
        metadata:
          name: busybox
          labels:
            app: busybox-pod
        spec:
          containers:
          - name: busybox-host
            image: busybox:latest
            command: ["sleep"]
            args: ["1000"]
    ...
    [root@host131 ReplicaSet]#

RC生成和结果确认

[root@host131 ReplicaSet]# kubectl create -f busybox-rc.yaml 
    replicationcontroller/test-rc created
    [root@host131 ReplicaSet]# 
    [root@host131 ReplicaSet]# kubectl get rc -o wide
    NAME      DESIRED   CURRENT   READY   AGE   CONTAINERS     IMAGES           SELECTOR
    test-rc   1         1         1       8s    busybox-host   busybox:latest   app=busybox-pod
    [root@host131 ReplicaSet]# 
    [root@host131 ReplicaSet]# kubectl get pods -o wide
    NAME            READY   STATUS    RESTARTS   AGE   IP             NODE              NOMINATED NODE   READINESS GATES
    test-rc-t4t57   1/1     Running   0          15s   10.254.152.5   192.168.163.131   <none>           <none>
    [root@host131 ReplicaSet]# kubectl exec -it test-rc-t4t57 sh
    / # hostname
    test-rc-t4t57
    / # ps -ef
    PID   USER     TIME  COMMAND
        1 root      0:00 sleep 1000
       11 root      0:00 sh
       17 root      0:00 ps -ef
    / #

# 使用示例: RS #

我们直接将上述RC的YAML文件进行修改来生成RS的YAML文件，来确认一下两者的区别，首先直接修改Kind

[root@host131 ReplicaSet]# kubectl create -f busybox-rs.yaml 
    error: unable to recognize "busybox-rs.yaml": no matches for kind "ReplicaSet" in version "v1"
    [root@host131 ReplicaSet]#

RS在apps/v1，修改之后继续确认，spec规格中需要添加selector

[root@host131 ReplicaSet]# diff busybox-r*
    2,3c2,3
    < apiVersion: v1
    < kind: ReplicationController
    ---
    > apiVersion: apps/v1
    > kind: ReplicaSet
    [root@host131 ReplicaSet]# kubectl create -f busybox-rs.yaml 
    error: error validating "busybox-rs.yaml": error validating data: ValidationError(ReplicaSet.spec.selector): unknown field "app" in io.k8s.apimachinery.pkg.apis.meta.v1.LabelSelector; if you choose to ignore these errors, turn validation off with --validate=false
    [root@host131 ReplicaSet]#

进行如下修改，添加matchLabels即可，这里将name也进行修改

[root@host131 ReplicaSet]# diff busybox-r*
    2,3c2,3
    < apiVersion: v1
    < kind: ReplicationController
    ---
    > apiVersion: apps/v1
    > kind: ReplicaSet
    5c5
    <   name: test-rc
    ---
    >   name: test-rs
    9c9,10
    <     app: busybox-pod
    ---
    >     matchLabels:
    >       app: busybox-pod
    [root@host131 ReplicaSet]#

YAML文件详细如下：

[root@host131 ReplicaSet]# cat busybox-rs.yaml 
    ---
    apiVersion: apps/v1
    kind: ReplicaSet
    metadata:
      name: test-rs
    spec:
      replicas: 1
      selector:
        matchLabels:
          app: busybox-pod
      template:
        metadata:
          name: busybox
          labels:
            app: busybox-pod
        spec:
          containers:
          - name: busybox-host
            image: busybox:latest
            command: ["sleep"]
            args: ["1000"]
    ...
    [root@host131 ReplicaSet]#

RS生成和结果确认

[root@host131 ReplicaSet]# kubectl get rs -o wide
    NAME      DESIRED   CURRENT   READY   AGE   CONTAINERS     IMAGES           SELECTOR
    test-rs   1         1         1       7s    busybox-host   busybox:latest   app=busybox-pod
    [root@host131 ReplicaSet]# 
    [root@host131 ReplicaSet]# kubectl get pod -o wide
    NAME            READY   STATUS    RESTARTS   AGE   IP             NODE              NOMINATED NODE   READINESS GATES
    test-rs-vfcdw   1/1     Running   0          15s   10.254.152.5   192.168.163.131   <none>           <none>
    [root@host131 ReplicaSet]# 
    [root@host131 ReplicaSet]# kubectl exec -it test-rs-vfcdw sh
    / # hostname
    test-rs-vfcdw
    / # ps -ef
    PID   USER     TIME  COMMAND
        1 root      0:00 sleep 1000
        6 root      0:00 sh
       12 root      0:00 ps -ef
    / #

# 总结 #

可以看到RC和RS的基本使用方式大体一致，只需要改一下Kind和selector即可，另外RS虽然可以创建并使用，但是在实际中更多情况则是直接使用Deployment。

# 参考内容 #

https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller/  
https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/