写在前面

通过POD 应用就有了存在的形式，通过deployment 保证了POD在一定的数量，通过service 可以实现一定数量的POD以负载均衡的方式对外提供服务。但，如果是程序开发了新功能，需要上线，该怎么办呢？对此k8s提供了平滑升级的解决方案，本文就一起来看下吧！

1：k8的版本是什么

在正式开始前，我们还需要看下什么是版本。在我们日常开发中完成一个功能后，一般都会在git上打一个tag，比如tag-v1.0，之后可能还会有其它版本，如下图：

这就是程序的版本，那么对于k8s来说版本是什么呢？当然肯定不是git这里的版本，而是yaml文件POD的template内容，但是yaml文件可能很大，总不能将其整个内容作为版本号吧，自然是不可以的，所以k8s采用的方案是将template部分执行hash得到一个一定长度的字符串，如下:

dongyunqi@mongodaddy:~/k8s$ kubectl get pod
NAME                      READY   STATUS    RESTARTS   AGE
ngx-dep-name-bfbb5f64b-ds78j   1/1     Running   0          6s
ngx-dep-name-bfbb5f64b-xr6gw   1/1     Running   0          6s

NAME列中的bfbb5f64b就是哈希template后的版本号了。

2：如何平滑升级

这里我们使用Nginx的镜像来测试，首先定义个ConfigMap，如下：

apiVersion: v1
kind: ConfigMap
metadata:
  name: ngx-conf

data:
  default.conf: |
    server {
      listen 80;
      location / {
        default_type text/plain;
        return 200
          'ver : $nginx_version\nsrv : $server_addr:$server_port\nhost: $hostname\n';
      }
    }

apply：

dongyunqi@mongodaddy:~/k8s$ kubectl apply -f smooth-upgrade-cm.yml 
configmap/ngx-conf created
dongyunqi@mongodaddy:~/k8s$ kubectl get cm
NAME               DATA   AGE
ngx-conf           1      8s

接着我们来创建deployment，yaml如下：

dongyunqi@mongodaddy:~/k8s$ cat smooth-upgrade-deployment.yml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: ngx-dep-app
  name: ngx-dep-name

spec:
  replicas: 3
  selector:
    matchLabels:
      app: ngx-dep-pod

  template:
    metadata:
      labels:
        app: ngx-dep-pod
    spec:
      volumes:
      - name: ngx-conf-vol
        configMap:
          name: ngx-conf

      containers:
      - image: nginx:alpine
        name: nginx
        ports:
        - containerPort: 80

        volumeMounts:
        - mountPath: /etc/nginx/conf.d
          name: ngx-conf-vol

apply后查看如下：

dongyunqi@mongodaddy:~/k8s$ kubectl apply -f smooth-upgrade-deployment.yml 
deployment.apps/ngx-dep-name created
dongyunqi@mongodaddy:~/k8s$ kubectl get deployment
NAME           READY   UP-TO-DATE   AVAILABLE   AGE
ngx-dep-name   3/3     3            3           5s

看下POD：

dongyunqi@mongodaddy:~/k8s$ kubectl get pod -l app=ngx-dep-pod
NAME                           READY   STATUS    RESTARTS   AGE
ngx-dep-name-dcc8b7bfd-bhksq   1/1     Running   0          111s
ngx-dep-name-dcc8b7bfd-t96np   1/1     Running   0          111s
ngx-dep-name-dcc8b7bfd-tsvmc   1/1     Running   0          111s

可以看到此时的版本号是dcc8b7bfd，但此时我们还不能访问POD，需要继续定义service，yaml如下：

dongyunqi@mongodaddy:~/k8s$ cat smooth-upgrade-service.yml 
apiVersion: v1
kind: Service
metadata:
  name: ngx-svc
  
spec:
  selector:
    app: ngx-dep-pod # 查找app label为ngx-dep-pod的POD
    
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP

以上service的80端口映射到后端POD们的80端口。

apply后查看如下：

dongyunqi@mongodaddy:~/k8s$ kubectl apply -f smooth-upgrade-service.yml 
service/ngx-svc created
dongyunqi@mongodaddy:~/k8s$ kubectl get service
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP   11d
ngx-svc      ClusterIP   10.99.187.192   <none>        80/TCP    6s
dongyunqi@mongodaddy:~/k8s$ kubect describe service ngx-svc
kubect: command not found
dongyunqi@mongodaddy:~/k8s$ kubectl describe service ngx-svc
Name:              ngx-svc
Namespace:         default
Labels:            <none>
Annotations:       <none>
Selector:          app=ngx-dep-pod
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                10.99.187.192
IPs:               10.99.187.192
Port:              <unset>  80/TCP
TargetPort:        80/TCP
Endpoints:         10.10.4.10:80,10.10.4.11:80,10.10.4.12:80
Session Affinity:  None
Events:            <none>

接着为了能够在外部访问我们使用port-forward来转发Node的8080端口到service的80端口，如下:

dongyunqi@mongodaddy:~/k8s$ kubectl port-forward svc/ngx-svc 8080:80 &
[1] 115371
dongyunqi@mongodaddy:~/k8s$ Forwarding from 127.0.0.1:8080 -> 80
Forwarding from [::1]:8080 -> 80

然后就可以访问了，如下：

dongyunqi@mongodaddy:~/k8s$ curl 127.0.0.1:8080
Handling connection for 8080
ver : 1.21.5
srv : 127.0.0.1:80
host: ngx-dep-name-dcc8b7bfd-bhksq

可以看到此时Nginx的版本号是1.21.5，接着我们来修改Nginx的版本号为nginx:1.22-alpine模拟应用的升级，deployment的yaml修改后如下：

dongyunqi@mongodaddy:~/k8s$ cat smooth-upgrade-deploymentv2.yml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: ngx-dep-app
  name: ngx-dep-name

spec:
  minReadySeconds: 15      # 确认Pod就绪的等待时间 
  replicas: 3
  selector:
    matchLabels:
      app: ngx-dep-pod

  template:
    metadata:
      labels:
        app: ngx-dep-pod
    spec:
      volumes:
      - name: ngx-conf-vol
        configMap:
          name: ngx-conf

      containers:
      - image: nginx:1.22-alpine
        name: nginx
        ports:
        - containerPort: 80

        volumeMounts:
        - mountPath: /etc/nginx/conf.d
          name: ngx-conf-vol

这里增加了minReadySeconds: 15来增加POD创建的间隔时间，不然k8s升级POD过快，不方便看到整个平滑升级的过程，接着apply：

dongyunqi@mongodaddy:~/k8s$ kubectl apply -f smooth-upgrade-deploymentv2.yml 
deployment.apps/ngx-dep-name configured

然后通过命令kubectl rollout status deployment ngx-dep-name来查看升级的过程：

dongyunqi@mongodaddy:~/k8s$ kubectl rollout status deployment ngx-dep-name
Waiting for deployment "ngx-dep-name" rollout to finish: 1 out of 3 new replicas have been updated...
Waiting for deployment "ngx-dep-name" rollout to finish: 1 out of 3 new replicas have been updated...
Waiting for deployment "ngx-dep-name" rollout to finish: 1 out of 3 new replicas have been updated...
Waiting for deployment "ngx-dep-name" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "ngx-dep-name" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "ngx-dep-name" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "ngx-dep-name" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "ngx-dep-name" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "ngx-dep-name" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "ngx-dep-name" rollout to finish: 1 old replicas are pending termination...
deployment "ngx-dep-name" successfully rolled out

以上展示了新POD的升级和老POD的销毁过程，我们也可以通过命令kubectl describe deploy ngx-dep-name来查看整个升级的过程，如下：

dongyunqi@mongodaddy:~/k8s$ kubectl describe deploy ngx-dep-name
...
Events:
  Type    Reason             Age    From                   Message
  ----    ------             ----   ----                   -------
  Normal  ScalingReplicaSet  33m    deployment-controller  Scaled up replica set ngx-dep-name-dcc8b7bfd to 3
  Normal  ScalingReplicaSet  11m    deployment-controller  Scaled up replica set ngx-dep-name-7cfd649b6 to 1
  Normal  ScalingReplicaSet  10m    deployment-controller  Scaled down replica set ngx-dep-name-dcc8b7bfd to 2
  Normal  ScalingReplicaSet  10m    deployment-controller  Scaled up replica set ngx-dep-name-7cfd649b6 to 2
  Normal  ScalingReplicaSet  10m    deployment-controller  Scaled down replica set ngx-dep-name-dcc8b7bfd to 1
  Normal  ScalingReplicaSet  10m    deployment-controller  Scaled up replica set ngx-dep-name-7cfd649b6 to 3
  Normal  ScalingReplicaSet  9m45s  deployment-controller  Scaled down replica set ngx-dep-name-dcc8b7bfd to 0

每一行的含义如下：

Scaled up replica set ngx-dep-name-dcc8b7bfd to 3
    老版本POD有3个
Scaled up replica set ngx-dep-name-7cfd649b6 to 1
    新版本POD增加到1个
Scaled down replica set ngx-dep-name-dcc8b7bfd to 2
    老版本POD减少到2个
Scaled up replica set ngx-dep-name-7cfd649b6 to 2    
    新版本POD增加到2个
Scaled down replica set ngx-dep-name-dcc8b7bfd to 1
    老版本POD减少到1个
Scaled up replica set ngx-dep-name-7cfd649b6 to 3
    新版本POD增加到3个
Scaled down replica set ngx-dep-name-dcc8b7bfd to 0
    老版本POD减少到0个

整个过程新POD的个数就好像滚雪球一样越来越多，所以这个过程也被称为滚动更新，整个过程用图展示的话如下：

接着我们可以查看新POD的版本信息：

dongyunqi@mongodaddy:~/k8s$ kubectl get pod -l app=ngx-dep-pod
NAME                           READY   STATUS    RESTARTS   AGE
ngx-dep-name-7cfd649b6-6ddnk   1/1     Running   0          5m23s
ngx-dep-name-7cfd649b6-fslcz   1/1     Running   0          3m45s
ngx-dep-name-7cfd649b6-pwd5r   1/1     Running   0          4m2s

可以看到此时版本变成了7cfd649b6，也可以访问确认Nginx升级是否成功：

dongyunqi@mongodaddy:~/k8s$ Forwarding from 127.0.0.1:8080 -> 80
Forwarding from [::1]:8080 -> 80

dongyunqi@mongodaddy:~/k8s$ curl 127.0.0.1:8080
Handling connection for 8080
ver : 1.22.1
srv : 127.0.0.1:80
host: ngx-dep-name-7cfd649b6-6ddnk

可以看到此时Nginx的版本号就变成了1.22.1了，说明Nginx就升级成功了。

3：更新历史维护

系统升级后并非万事大吉，因为可能会因为一个严重的bug需要我们将应用回退到之前的版本，k8s针对这种情况也提供了对应的解决方案，具体是使用命令kubectl rollout，如下查看更新历史：

dongyunqi@mongodaddy:~/k8s$ kubectl rollout history deploy ngx-dep-name
deployment.apps/ngx-dep-name 
REVISION  CHANGE-CAUSE
1         <none>
2         <none>

可以看到此时我们有1和2两个版本，但CHANGE-CAUSE是<none>，就好像提交的代码没有comment一样，多少有些别扭，想要让该列有值需要在deployment的metadata中增加annotations: kubernetes.io/change-cause: 更新原因，为了测试，我们再来对Nginx进行一次升级，使用版本1.23.3,修改后yaml如下：

dongyunqi@mongodaddy:~/k8s$ cat smooth-upgrade-deploymentv3.yml
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: ngx-dep-app
  name: ngx-dep-name
  annotations:
    kubernetes.io/change-cause: upgrade ngixn to 1.23.3  # ***

spec:
  replicas: 3
  selector:
    matchLabels:
      app: ngx-dep-pod

  template:
    metadata:
      labels:
        app: ngx-dep-pod
    spec:
      volumes:
      - name: ngx-conf-vol
        configMap:
          name: ngx-conf

      containers:
      - image: nginx:1.23.3 # ***
        name: nginx
        ports:
        - containerPort: 80

        volumeMounts:
        - mountPath: /etc/nginx/conf.d
          name: ngx-conf-vol

***为修改的行。apply后再来查看更新历史：

dongyunqi@mongodaddy:~/k8s$ kubectl rollout history deploy ngx-dep-name
deployment.apps/ngx-dep-name 
REVISION  CHANGE-CAUSE
1         <none>
2         <none>
3         upgrade ngixn to 1.23.3

可以看到此时CHANGE-CAUSE就有值了(看着舒服多了),有了这个更新历史之后，就可以使用命令 kubectl rollout undo，也可以加上参数 --to-revision 回退到任意一个历史版本，如下回退到最老的版本1:

dongyunqi@mongodaddy:~/k8s$ kubectl rollout undo deploy ngx-dep-name --to-revision=1
deployment.apps/ngx-dep-name rolled back

写在后面

小结

本文我们一起看了k8s的平滑升级方案，并分析了滚动更新的具体过程，查看了更新历史，以及如何回滚更新到指定版本等内容。希望本文能够帮助到你。

参考文章列表

k8s之Service 。