K8s中RS和Deployment

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。

[root@k8s-master mnt]# cat rs.yaml
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: frontend
spec:
  replicas: 3
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        tier: frontend
    spec:
      containers:
      - name: myapp
        image: wangyanglinux/myapp:v1
        env:
        - name: GET_HOSTS_FROM
          value: dns
        ports:
        - containerPort: 80
[root@k8s-master mnt]#

[root@k8s-master mnt]# kubectl create -f rs.yaml
replicaset.apps/frontend created
[root@k8s-master mnt]# kubectl get pod
NAME             READY   STATUS    RESTARTS   AGE
frontend-4xs95   1/1     Running   0          12s
frontend-gd5th   1/1     Running   0          12s
frontend-tn9pn   1/1     Running   0          12s
[root@k8s-master mnt]# kubectl delete pod --all
pod "frontend-4xs95" deleted
pod "frontend-gd5th" deleted
pod "frontend-tn9pn" deleted
[root@k8s-master mnt]# kubectl get pod
NAME             READY   STATUS    RESTARTS   AGE
frontend-gh2w5   1/1     Running   0          3m58s
frontend-rd9pl   1/1     Running   0          3m58s
frontend-xg845   1/1     Running   0          3m58s
[root@k8s-master mnt]# kubectl get pod --show-labels
NAME             READY   STATUS    RESTARTS   AGE     LABELS
frontend-gh2w5   1/1     Running   0          4m38s   tier=frontend
frontend-rd9pl   1/1     Running   0          4m38s   tier=frontend
frontend-xg845   1/1     Running   0          4m38s   tier=frontend
[root@k8s-master mnt]# kubectl get pod --show-labels
NAME             READY   STATUS    RESTARTS   AGE     LABELS
frontend-btqh8   1/1     Running   0          3s      tier=frontend
frontend-gh2w5   1/1     Running   0          7m43s   tier=frontend
frontend-rd9pl   1/1     Running   0          7m43s   tier=frontend1
frontend-xg845   1/1     Running   0          7m43s   tier=frontend
[root@k8s-master mnt]# kubectl delete pod --all
pod "frontend-btqh8" deleted
pod "frontend-gh2w5" deleted
pod "frontend-rd9pl" deleted
pod "frontend-xg845" deleted
[root@k8s-master mnt]# kubectl get pod --show-labels
NAME             READY   STATUS    RESTARTS   AGE   LABELS
frontend-mnmlm   1/1     Running   0          28s   tier=frontend
frontend-x8rcp   1/1     Running   0          27s   tier=frontend
frontend-zqs4n   1/1     Running   0          28s   tier=frontend
[root@k8s-master mnt]# kubectl delete -f rs.yaml
replicaset.apps "frontend" deleted
[root@k8s-master mnt]# kubectl get pod --show-labels
NAME             READY   STATUS        RESTARTS   AGE   LABELS
frontend-mnmlm   0/1     Terminating   0          47s   tier=frontend
frontend-x8rcp   0/1     Terminating   0          46s   tier=frontend
frontend-zqs4n   0/1     Terminating   0          47s   tier=frontend

Deployment是什么？

Deployment为Pod和Replica Set（下一代Replication Controller）提供声明式更新。

你只需要在Deployment中描述你想要的目标状态是什么，Deployment controller就会帮你将Pod和Replica Set的实际状态改变到你的目标状态。你可以定义一个全新的Deployment，也可以创建一个新的替换旧的Deployment。

一个典型的用例如下：

• 使用Deployment来创建ReplicaSet。ReplicaSet在后台创建pod。检查启动状态，看它是成功还是失败。
• 然后，通过更新Deployment的PodTemplateSpec字段来声明Pod的新状态。这会创建一个新的ReplicaSet，Deployment会按照控制的速率将pod从旧的ReplicaSet移动到新的ReplicaSet中。
• 如果当前状态不稳定，回滚到之前的Deployment revision。每次回滚都会更新Deployment的revision。
• 扩容Deployment以满足更高的负载。
• 暂停Deployment来应用PodTemplateSpec的多个修复，然后恢复上线。
• 根据Deployment 的状态判断上线是否hang住了。
• 清除旧的不必要的ReplicaSet。

 代码展示：

[root@k8s-master mnt]# cat deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 3
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: wangyanglinux/myapp:v1
        ports:
        - containerPort: 80
[root@k8s-master mnt]#

下面的代码包括了扩容和回退和更新。

[root@k8s-master mnt]# kubectl apply -f deployment.yaml --record
deployment.apps/nginx-deployment created
[root@k8s-master mnt]# kubectl get pod
NAME                                READY   STATUS              RESTARTS   AGE
nginx-deployment-64ddb75745-fkfxl   0/1     ContainerCreating   0          1s
nginx-deployment-64ddb75745-slcwp   0/1     ContainerCreating   0          1s
nginx-deployment-64ddb75745-vwnqw   0/1     ContainerCreating   0          1s
[root@k8s-master mnt]# kubectl get pod
NAME                                READY   STATUS    RESTARTS   AGE
nginx-deployment-64ddb75745-fkfxl   1/1     Running   0          55s
nginx-deployment-64ddb75745-slcwp   1/1     Running   0          55s
nginx-deployment-64ddb75745-vwnqw   1/1     Running   0          55s
[root@k8s-master mnt]# kubectl get rs
NAME                          DESIRED   CURRENT   READY   AGE
nginx-deployment-64ddb75745   3         3         3       65s
[root@k8s-master mnt]# kubectl get pod -o wide
NAME                                READY   STATUS    RESTARTS   AGE     IP           NODE         NOMINATED NODE   READINESS GATES
nginx-deployment-64ddb75745-fkfxl   1/1     Running   0          2m45s   10.244.2.6   k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-slcwp   1/1     Running   0          2m45s   10.244.1.9   k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-vwnqw   1/1     Running   0          2m45s   10.244.1.8   k8s-node02   <none>           <none>
[root@k8s-master mnt]# curl 10.244.2.6
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[root@k8s-master mnt]# kubectl scale deployment nginx-deployment --replicas 10
deployment.apps/nginx-deployment scaled
[root@k8s-master mnt]# kubectl get pod -o wide
NAME                                READY   STATUS              RESTARTS   AGE     IP           NODE         NOMINATED NODE   READINESS GATES
nginx-deployment-64ddb75745-9c55m   0/1     ContainerCreating   0          3s      <none>       k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-9gs9v   0/1     ContainerCreating   0          3s      <none>       k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-fkfxl   1/1     Running             0          4m10s   10.244.2.6   k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-nbl92   0/1     ContainerCreating   0          3s      <none>       k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-p4f2z   0/1     ContainerCreating   0          3s      <none>       k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-qtmhl   0/1     ContainerCreating   0          3s      <none>       k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-rgcsl   0/1     ContainerCreating   0          3s      <none>       k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-slcwp   1/1     Running             0          4m10s   10.244.1.9   k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-vwnqw   1/1     Running             0          4m10s   10.244.1.8   k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-zzmsn   0/1     ContainerCreating   0          3s      <none>       k8s-node01   <none>           <none>
[root@k8s-master mnt]# kubectl describe deployment
Name:                   nginx-deployment
Namespace:              default
CreationTimestamp:      Fri, 20 Dec 2019 15:10:03 +0800
Labels:                 <none>
Annotations:            deployment.kubernetes.io/revision: 1
                        kubectl.kubernetes.io/last-applied-configuration:
                          {"apiVersion":"apps/v1","kind":"Deployment","metadata":{"annotations":{"kubernetes.io/change-cause":"kubectl apply --filename=de     ployment.y...
                        kubernetes.io/change-cause: kubectl apply --filename=deployment.yaml --record=true
Selector:               app=nginx
Replicas:               10 desired | 10 updated | 10 total | 10 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
  Labels:  app=nginx
  Containers:
   nginx:
    Image:        wangyanglinux/myapp:v1
    Port:         80/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Progressing    True    NewReplicaSetAvailable
  Available      True    MinimumReplicasAvailable
OldReplicaSets:  <none>
NewReplicaSet:   nginx-deployment-64ddb75745 (10/10 replicas created)
Events:
  Type    Reason             Age    From                   Message
  ----    ------             ----   ----                   -------
  Normal  ScalingReplicaSet  11m    deployment-controller  Scaled up replica set nginx-deployment-64ddb75745 to 3
  Normal  ScalingReplicaSet  7m28s  deployment-controller  Scaled up replica set nginx-deployment-64ddb75745 to 10
[root@k8s-master mnt]# kubectl rollout history deployment/nginx-deployment
deployment.apps/nginx-deployment
REVISION  CHANGE-CAUSE
1         kubectl apply --filename=deployment.yaml --record=true

[root@k8s-master mnt]# kubectl set image deployment/nginx-deployment nginx=wangyanglinux/myapp:v2
deployment.apps/nginx-deployment image updated
[root@k8s-master mnt]# kubectl get pod -o wide
NAME                                READY   STATUS        RESTARTS   AGE   IP            NODE         NOMINATED NODE   READINESS GATES
nginx-deployment-64ddb75745-rgcsl   0/1     Terminating   0          30m   10.244.1.12   k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-slcwp   0/1     Terminating   0          35m   10.244.1.9    k8s-node02   <none>           <none>
nginx-deployment-6bd7755b5b-2qwdf   1/1     Running       0          23s   10.244.2.12   k8s-node01   <none>           <none>
nginx-deployment-6bd7755b5b-2tpzn   1/1     Running       0          23s   10.244.2.11   k8s-node01   <none>           <none>
nginx-deployment-6bd7755b5b-5d2fn   1/1     Running       0          23s   10.244.1.14   k8s-node02   <none>           <none>
nginx-deployment-6bd7755b5b-87vdh   1/1     Running       0          23s   10.244.2.13   k8s-node01   <none>           <none>
nginx-deployment-6bd7755b5b-fl56p   1/1     Running       0          14s   10.244.1.16   k8s-node02   <none>           <none>
nginx-deployment-6bd7755b5b-gpz9q   1/1     Running       0          12s   10.244.1.17   k8s-node02   <none>           <none>
nginx-deployment-6bd7755b5b-hhfbn   1/1     Running       0          11s   10.244.2.15   k8s-node01   <none>           <none>
nginx-deployment-6bd7755b5b-k5rm7   1/1     Running       0          23s   10.244.1.13   k8s-node02   <none>           <none>
nginx-deployment-6bd7755b5b-skh7w   1/1     Running       0          14s   10.244.1.15   k8s-node02   <none>           <none>
nginx-deployment-6bd7755b5b-t494q   1/1     Running       0          13s   10.244.2.14   k8s-node01   <none>           <none>
[root@k8s-master mnt]# curl 10.244.1.14
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
[root@k8s-master mnt]# kubectl get rs
NAME                          DESIRED   CURRENT   READY   AGE
nginx-deployment-64ddb75745   0         0         0       35m
nginx-deployment-6bd7755b5b   10        10        10      64s
[root@k8s-master mnt]# kubectl rollout undo deployment/nginx-deployment
deployment.apps/nginx-deployment rolled back
[root@k8s-master mnt]# kubectl get pod
NAME                                READY   STATUS              RESTARTS   AGE
nginx-deployment-64ddb75745-48d5d   1/1     Running             0          11s
nginx-deployment-64ddb75745-4ctzd   1/1     Running             0          13s
nginx-deployment-64ddb75745-8g7f9   1/1     Running             0          13s
nginx-deployment-64ddb75745-bnwlj   1/1     Running             0          9s
nginx-deployment-64ddb75745-gq29d   1/1     Running             0          13s
nginx-deployment-64ddb75745-rp52v   1/1     Running             0          13s
nginx-deployment-64ddb75745-sxch9   1/1     Running             0          10s
nginx-deployment-64ddb75745-tt8tp   0/1     ContainerCreating   0          5s
nginx-deployment-64ddb75745-vtx8w   1/1     Running             0          13s
nginx-deployment-64ddb75745-zr8c7   1/1     Running             0          7s
nginx-deployment-6bd7755b5b-2qwdf   1/1     Terminating         0          3m14s
nginx-deployment-6bd7755b5b-2tpzn   1/1     Terminating         0          3m14s
nginx-deployment-6bd7755b5b-87vdh   1/1     Terminating         0          3m14s
[root@k8s-master mnt]# kubectl get rs
NAME                          DESIRED   CURRENT   READY   AGE
nginx-deployment-64ddb75745   10        10        10      38m
nginx-deployment-6bd7755b5b   0         0         0       3m29s
[root@k8s-master mnt]# kubectl get pod -o wide
NAME                                READY   STATUS    RESTARTS   AGE   IP            NODE         NOMINATED NODE   READINESS GATES
nginx-deployment-64ddb75745-48d5d   1/1     Running   0          43s   10.244.2.18   k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-4ctzd   1/1     Running   0          45s   10.244.1.18   k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-8g7f9   1/1     Running   0          45s   10.244.1.19   k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-bnwlj   1/1     Running   0          41s   10.244.1.21   k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-gq29d   1/1     Running   0          45s   10.244.2.17   k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-rp52v   1/1     Running   0          45s   10.244.1.20   k8s-node02   <none>           <none>
nginx-deployment-64ddb75745-sxch9   1/1     Running   0          42s   10.244.2.19   k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-tt8tp   1/1     Running   0          37s   10.244.2.20   k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-vtx8w   1/1     Running   0          45s   10.244.2.16   k8s-node01   <none>           <none>
nginx-deployment-64ddb75745-zr8c7   1/1     Running   0          39s   10.244.1.22   k8s-node02   <none>           <none>
[root@k8s-master mnt]# curl 10.244.2.19
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[root@k8s-master mnt]# kubectl rollout status deployment/nginx-deployment
deployment "nginx-deployment" successfully rolled out
[root@k8s-master mnt]# kubectl rollout history deployment/nginx-deployment
deployment.apps/nginx-deployment
REVISION  CHANGE-CAUSE
2         kubectl apply --filename=deployment.yaml --record=true
3         kubectl apply --filename=deployment.yaml --record=true