k8s滚动更新（8）

一、k8s版本更新

　　滚动更新是一次只更新一小部分副本，成功后，再更新更多的副本，最终完成所有副本的更新。滚动更新的最大的好处是零停机，整个更新过程始终有副本在运行，从而保证了业务的连续性。

　　实践：部署三个副本应用，初始镜像为httpd:v1，然后将其更新到httpd：v3

1、httpd:v1的配置文件如下：

[root@ren7 yaml]# cat httpdv1.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: httpdv1
spec:
  replicas: 3
  template:
    metadata:
      labels:
        name: httpdv1
        run: httpd
    spec:
      containers:
      - name: httpd-appv1
        image: reg.yunwei.com/learn/httpd:v1
        ports:
        - containerPort: 80

2、部署应用并查看

[root@ren7 yaml]# kubectl apply -f httpdv1.yaml
deployment.extensions/httpdv1 created
[root@ren7 yaml]# kubectl get deployment -o wide
NAME      READY   UP-TO-DATE   AVAILABLE   AGE   CONTAINERS    IMAGES                          SELECTOR
httpdv1   3/3     3            3           19s   httpd-appv1   reg.yunwei.com/learn/httpd:v1   name=httpdv1,run=httpd
[root@ren7 yaml]# kubectl get replicaset -o wide
NAME                 DESIRED   CURRENT   READY   AGE   CONTAINERS    IMAGES                          SELECTOR
httpdv1-676f9f5d8f   3         3         3       46s   httpd-appv1   reg.yunwei.com/learn/httpd:v1   name=httpdv1,pod-template-hash=676f9f5d8f,run=httpd
[root@ren7 yaml]# kubectl get pod -o wide
NAME                       READY   STATUS    RESTARTS   AGE   IP              NODE           NOMINATED NODE   READINESS GATES
httpdv1-676f9f5d8f-9jmxx   1/1     Running   0          59s   172.20.33.97    192.168.11.6   <none>           <none>
httpdv1-676f9f5d8f-ldmbk   1/1     Running   0          59s   172.20.72.187   192.168.11.5   <none>           <none>
httpdv1-676f9f5d8f-m8w82   1/1     Running   0          59s   172.20.72.188   192.168.11.5   <none>           <none>

　　部署过程如下：

　　创建 Deployment httpdv1

　　创建 ReplicaSet httpdv1-676f9f5d8f

　　创建三个 Pod

　　当前镜像为 reg.yunwei.com/learn/httpd:v1

3、将配置文件中 reg.yunwei.com/learn/httpd:v1 替换为 reg.yunwei.com/learn/httpd:v2，再次执行 kubectl apply。

[root@ren7 yaml]# vim httpdv1.yaml
[root@ren7 yaml]# kubectl apply -f httpdv1.yaml
deployment.extensions/httpdv1 configured
[root@ren7 yaml]# kubectl get deployment -o wide
NAME      READY   UP-TO-DATE   AVAILABLE   AGE     CONTAINERS    IMAGES                          SELECTOR
httpdv1   2/3     3            2           4m17s   httpd-appv1   reg.yunwei.com/learn/httpd:v2   name=httpdv1,run=httpd
[root@ren7 yaml]# kubectl get replicaset -o wide　　　　#这一步要稍微等几分钟才会切换到v2版本
NAME                 DESIRED   CURRENT   READY   AGE     CONTAINERS    IMAGES                          SELECTOR
httpdv1-676f9f5d8f   0         0         0       4m56s   httpd-appv1   reg.yunwei.com/learn/httpd:v1   name=httpdv1,pod-template-hash=676f9f5d8f,run=httpd
httpdv1-75f7c775db   3         3         3       43s     httpd-appv1   reg.yunwei.com/learn/httpd:v2   name=httpdv1,pod-template-hash=75f7c775db,run=httpd
[root@ren7 yaml]# kubectl get pod -o wide
NAME                       READY   STATUS    RESTARTS   AGE   IP              NODE           NOMINATED NODE   READINESS GATES
httpdv1-75f7c775db-44kpj   1/1     Running   0          49s   172.20.72.189   192.168.11.5   <none>           <none>
httpdv1-75f7c775db-dx2dn   1/1     Running   0          46s   172.20.33.99    192.168.11.6   <none>           <none>
httpdv1-75f7c775db-m9dnc   1/1     Running   0          49s   172.20.33.98    192.168.11.6   <none>           <none>

我们发现了如下变化：

　　Deployment httpdv1 的镜像更新为 reg.yunwei.com/learn/httpd:v2

　　新创建了 ReplicaSet httpdv1-75f7c775db ，镜像为 reg.yunwei.com/learn/httpd:v2，并且管理了三个新的 Pod。

　　之前的 ReplicaSet httpdv1-676f9f5d8f 里面已经没有任何 Pod。

　　结论是：ReplicaSet httpdv1-676f9f5d8f 的三个 reg.yunwei.com/learn/httpd:v1 Pod 已经被 ReplicaSet httpdv1-75f7c775db 的三个 reg.yunwei.com/learn/httpd:v2 Pod 替换了。

第四步：具体过程可以通过 kubectl describe deployment httpd 查看。

[root@ren7 yaml]# kubectl describe deployment httpdv1
Name:                   httpdv1
Namespace:              default
CreationTimestamp:      Sat, 26 Oct 2019 09:44:08 +0800
Labels:                 name=httpdv1
                        run=httpd
Annotations:            deployment.kubernetes.io/revision: 2
                        kubectl.kubernetes.io/last-applied-configuration:
                          {"apiVersion":"extensions/v1beta1","kind":"Deployment","metadata":{"annotations":{},"name":"httpdv1","namespace":"default"},"spec":{"repli...
Selector:               name=httpdv1,run=httpd
Replicas:               3 desired | 3 updated | 3 total | 3 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  1 max unavailable, 1 max surge
Pod Template:
  Labels:  name=httpdv1
           run=httpd
  Containers:
   httpd-appv1:
    Image:        reg.yunwei.com/learn/httpd:v2
    Port:         80/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Available      True    MinimumReplicasAvailable
OldReplicaSets:  <none>
NewReplicaSet:   httpdv1-75f7c775db (3/3 replicas created)
Events:
  Type    Reason             Age    From                   Message
  ----    ------             ----   ----                   -------
  Normal  ScalingReplicaSet  12m    deployment-controller  Scaled up replica set httpdv1-676f9f5d8f to 3
  Normal  ScalingReplicaSet  8m39s  deployment-controller  Scaled up replica set httpdv1-75f7c775db to 1
  Normal  ScalingReplicaSet  8m39s  deployment-controller  Scaled down replica set httpdv1-676f9f5d8f to 2
  Normal  ScalingReplicaSet  8m39s  deployment-controller  Scaled up replica set httpdv1-75f7c775db to 2
  Normal  ScalingReplicaSet  8m36s  deployment-controller  Scaled down replica set httpdv1-676f9f5d8f to 1
  Normal  ScalingReplicaSet  8m36s  deployment-controller  Scaled up replica set httpdv1-75f7c775db to 3
  Normal  ScalingReplicaSet  8m32s  deployment-controller  Scaled down replica set httpdv1-676f9f5d8f to 0

每次只更新替换一个 Pod：

　　ReplicaSet httpdv1-75f7c775db 增加一个 Pod，总数为 1。

　　ReplicaSet httpdv1-676f9f5d8f 减少一个 Pod，总数为 2。

　　ReplicaSet httpdv1-75f7c775db 增加一个 Pod，总数为 2。

　　ReplicaSet httpdv1-676f9f5d8f 减少一个 Pod，总数为 1。

　　ReplicaSet httpdv1-75f7c775db 增加一个 Pod，总数为 3。

　　ReplicaSet httpdv1-676f9f5d8f 减少一个 Pod，总数为 0。

　　每次替换的 Pod 数量是可以定制的。Kubernetes 提供了两个参数 maxSurge 和 maxUnavailable 来精细控制 Pod 的替换数量。

二、更新回滚

　　kubectl apply 每次更新应用时 Kubernetes 都会记录下当前的配置，保存为一个 revision（版次），这样就可以回滚到某个特定 revision。

　　默认配置下，Kubernetes 只会保留最近的几个 revision，可以在 Deployment 配置文件中通过 revisionHistoryLimit 属性增加 revision 数量。

实践：回滚功能

1、应用有如下三个配置文件httpdv1.yaml，httpdv2.yaml 和 httpdv3.yaml，分别对应不同的httpd的镜像v1，v2和v3：

[root@ren7 yaml]# cat httpdv1.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: httpd
spec:
  revisionHistoryLimit: 10
  replicas: 3
  template:
    metadata:
      labels:
        name: httpd
        run: httpd
    spec:
      containers:
      - name: httpd-app
        image: reg.yunwei.com/learn/httpd:v1
        ports:
        - containerPort: 80

[root@ren7 yaml]# cat httpdv2.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: httpd
spec:
  revisionHistoryLimit: 10
  replicas: 3
  template:
    metadata:
      labels:
        name: httpd
        run: httpd
    spec:
      containers:
      - name: httpd-app
        image: reg.yunwei.com/learn/httpd:v2
        ports:
        - containerPort: 80
#      nodeSelector:
#        disktype: ssd

[root@ren7 yaml]# cat httpdv3.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: httpd
spec:
  revisionHistoryLimit: 10
  replicas: 3
  template:
    metadata:
      labels:
        name: httpd
        run: httpd
    spec:
      containers:
      - name: httpd-app
        image: reg.yunwei.com/learn/httpd:v3
        ports:
        - containerPort: 80

2、部署应用并更新

　　后面一个部署的应用，会覆盖掉前面的（名称相同）

[root@ren7 yaml]# kubectl apply -f httpdv1.yaml --record
deployment.extensions/httpd created
[root@ren7 yaml]# kubectl get deployment httpd -o wide
NAME    READY   UP-TO-DATE   AVAILABLE   AGE   CONTAINERS   IMAGES                          SELECTOR
httpd   3/3     3            3           33s   httpd-app    reg.yunwei.com/learn/httpd:v1   name=httpd,run=httpd

[root@ren7 yaml]# kubectl apply -f httpdv2.yaml --record
deployment.extensions/httpd configured
[root@ren7 yaml]# kubectl get deployment httpd -o wide
NAME    READY   UP-TO-DATE   AVAILABLE   AGE   CONTAINERS   IMAGES                          SELECTOR
httpd   2/3     3            2           45s   httpd-app    reg.yunwei.com/learn/httpd:v2   name=httpd,run=httpd

[root@ren7 yaml]# kubectl apply -f httpdv3.yaml --record
deployment.extensions/httpd configured
[root@ren7 yaml]# kubectl get deployment httpd -o wide
NAME    READY   UP-TO-DATE   AVAILABLE   AGE   CONTAINERS   IMAGES                          SELECTOR
httpd   2/3     2            2           54s   httpd-app    reg.yunwei.com/learn/httpd:v3   name=httpd,run=httpd

　　--record 的作用是将当前命令记录到 revision 记录中，这样我们就可以知道每个 revison 对应的是哪个配置文件。

3、通过 kubectl rollout history deployment httpd 查看 revison 历史记录。

[root@ren7 yaml]# kubectl rollout history deployment httpd
deployment.extensions/httpd
REVISION  CHANGE-CAUSE
1         kubectl apply --filename=httpdv1.yaml --record=true
2         kubectl apply --filename=httpdv2.yaml --record=true
3         kubectl apply --filename=httpdv3.yaml --record=true

　　CHANGE-CAUSE 就是 --record 的结果。

4、如果要回滚到某个版本，比如 revision 1，可以执行命令 kubectl rollout undo deployment httpd --to-revision=1：

[root@ren7 yaml]# kubectl rollout undo deployment httpd --to-revision=1
deployment.extensions/httpd rolled back
[root@ren7 yaml]# kubectl get deployment httpd -o wide
NAME    READY   UP-TO-DATE   AVAILABLE   AGE     CONTAINERS   IMAGES                          SELECTOR
httpd   3/3     3            3           4m31s   httpd-app    reg.yunwei.com/learn/httpd:v1   name=httpd,run=httpd

5、此时，revison 历史记录也会发生相应变化。

[root@ren7 yaml]# kubectl rollout history deployment httpd
deployment.extensions/httpd
REVISION  CHANGE-CAUSE
2         kubectl apply --filename=httpdv2.yaml --record=true
3         kubectl apply --filename=httpdv3.yaml --record=true
4         kubectl apply --filename=httpdv1.yaml --record=true

　　revison 1 变成了 revison 4。不过我们可以通过 CHANGE-CAUSE 知道每个 revison 的具体含义。所以一定要在执行 kubectl apply 时加上 --record参数。