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。
