【Kubernetes】不帶to-revision的kubectl rollout undo存在無限死回圈問題-有解無憂

第一步，撰寫首次部署所需的yaml檔案，包括三塊：命名空間定義、服務定義、部署定義，nginx的鏡像版本為 1.16.1

內容如下：

apiVersion: v1
kind: Namespace
metadata:
  name: load-balance

---

kind: Service
apiVersion: v1
metadata:
  labels:
    app: nginx-1161
  name: nginx-1161
  namespace: load-balance
spec:
  type: NodePort
  ports:
    - port: 80
      targetPort: 80
      nodePort: 30012
  selector:
    app: nginx-1161

---

kind: Deployment
apiVersion: apps/v1
metadata:
  labels:
    app: nginx-1161
  name: nginx-1161
  namespace: load-balance
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx-1161
  template:
    metadata:
      labels:
        app: nginx-1161
    spec:
      containers:
      - name: nginx
        image: nginx:1.16.1
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 80
          protocol: TCP

# 執行創建
$ kubectl apply -f ./nginx-deployment.yaml 
namespace/load-balance created
service/nginx-1161 created
deployment.apps/nginx-1161 created

# 第一次創建的容器實體我們簡稱為“7d”
$ kubectl get pods -n load-balance
NAME                          READY   STATUS    RESTARTS   AGE
nginx-1161-7d57d5c7c4-prk5p   1/1     Running   0          22m
nginx-1161-7d57d5c7c4-s4pqk   1/1     Running   0          22m
nginx-1161-7d57d5c7c4-v42kt   1/1     Running   0          22m

# 測驗訪問Nginx的主頁，成功回傳Nginx歡迎頁面的html代碼
$ curl http://192.168.223.201:30012/
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

第二步，執行第一次滾動升級，修改Nginx鏡像的版本為1.18.0，增加滾動升級的模塊配置

apiVersion: v1
kind: Namespace
metadata:
  name: load-balance

---

kind: Service
apiVersion: v1
metadata:
  labels:
    app: nginx-1161
  name: nginx-1161
  namespace: load-balance
spec:
  type: NodePort
  ports:
    - port: 80
      targetPort: 80
      nodePort: 30012
  selector:
    app: nginx-1161

---

kind: Deployment
apiVersion: apps/v1
metadata:
  labels:
    app: nginx-1161
  name: nginx-1161
  namespace: load-balance
spec:
  minReadySeconds: 5     # 增加配置
  strategy:              # 增加配置
    type: RollingUpdate  # 增加配置
    rollingUpdate:       # 增加配置
      maxSurge: 1        # 增加配置
      maxUnavailable: 1  # 增加配置
  replicas: 3
  selector:
    matchLabels:
      app: nginx-1161
  template:
    metadata:
      labels:
        app: nginx-1161
    spec:
      containers:
      - name: nginx
        image: nginx:1.18.0   # 配置修改
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 80
          protocol: TCP

# 執行滾動升級
$ kubectl apply -f nginx-update-I-deployment.yaml
namespace/load-balance unchanged
service/nginx-1161 unchanged
deployment.apps/nginx-1161 configured

# 查看滾動升級的狀態
$ kubectl rollout status deployment nginx-1161 -n load-balance
deployment "nginx-1161" successfully rolled out

# 查看副本集（rs，即ReplicaSet）
$  kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   3         3         3       84s
nginx-1161-7d57d5c7c4   0         0         0       26m

# 查看pods和服務
$ kubectl get pods,svc -n load-balance
NAME                              READY   STATUS    RESTARTS   AGE
pod/nginx-1161-56dd96d66c-724rg   1/1     Running   0          119s
pod/nginx-1161-56dd96d66c-cnkn6   1/1     Running   0          81s
pod/nginx-1161-56dd96d66c-zhq4c   1/1     Running   0          119s

NAME                 TYPE       CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
service/nginx-1161   NodePort   10.96.92.254   <none>        80:30012/TCP   28m

第三步，執行第二次滾動升級，修改image的版本為 1.20.1

apiVersion: v1
kind: Namespace
metadata:
  name: load-balance

---

kind: Service
apiVersion: v1
metadata:
  labels:
    app: nginx-1161
  name: nginx-1161
  namespace: load-balance
spec:
  type: NodePort
  ports:
    - port: 80
      targetPort: 80
      nodePort: 30012
  selector:
    app: nginx-1161

---

kind: Deployment
apiVersion: apps/v1
metadata:
  labels:
    app: nginx-1161
  name: nginx-1161
  namespace: load-balance
spec:
  minReadySeconds: 5
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1
  replicas: 3
  selector:
    matchLabels:
      app: nginx-1161
  template:
    metadata:
      labels:
        app: nginx-1161
    spec:
      containers:
      - name: nginx
        image: nginx:1.20.1      # 配置修改
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 80
          protocol: TCP

$ kubectl apply -f nginx-update-II-deployment.yaml 
namespace/load-balance unchanged
service/nginx-1161 unchanged
deployment.apps/nginx-1161 configured

#  kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   2         2         2       3m46s
nginx-1161-7cccdf449f   2         2         0       17s
nginx-1161-7d57d5c7c4   0         0         0       29m

$ kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   2         2         2       4m2s
nginx-1161-7cccdf449f   2         2         1       33s
nginx-1161-7d57d5c7c4   0         0         0       29m

$ kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   1         1         1       4m8s
nginx-1161-7cccdf449f   3         3         1       39s
nginx-1161-7d57d5c7c4   0         0         0       29m

$ kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   1         1         1       4m13s
nginx-1161-7cccdf449f   3         3         2       44s
nginx-1161-7d57d5c7c4   0         0         0       29m

$  kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   0         0         0       4m15s
nginx-1161-7cccdf449f   3         3         2       46s
nginx-1161-7d57d5c7c4   0         0         0       29m

# 至此，滾動升級全部完成（資料抓取時間延后，非升級速度慢）
$ kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   0         0         0       26m
nginx-1161-7cccdf449f   3         3         3       23m
nginx-1161-7d57d5c7c4   0         0         0       52m

檢查歷史版本的詳細資訊：

$ kubectl rollout history  deployment nginx-1161 -n load-balance --revision=3
deployment.apps/nginx-1161 with revision #3
Pod Template:
  Labels:       app=nginx-1161
        pod-template-hash=7cccdf449f
  Containers:
   nginx:
    Image:      nginx:1.20.1
    Port:       80/TCP
    Host Port:  0/TCP
    Environment:        <none>
    Mounts:     <none>
  Volumes:      <none>

$ kubectl rollout history  deployment nginx-1161 -n load-balance --revision=2
deployment.apps/nginx-1161 with revision #2
Pod Template:
  Labels:       app=nginx-1161
        pod-template-hash=56dd96d66c
  Containers:
   nginx:
    Image:      nginx:1.18.0
    Port:       80/TCP
    Host Port:  0/TCP
    Environment:        <none>
    Mounts:     <none>
  Volumes:      <none>

$ kubectl rollout history  deployment nginx-1161 -n load-balance --revision=1
deployment.apps/nginx-1161 with revision #1
Pod Template:
  Labels:       app=nginx-1161
        pod-template-hash=7d57d5c7c4
  Containers:
   nginx:
    Image:      nginx:1.16.1
    Port:       80/TCP
    Host Port:  0/TCP
    Environment:        <none>
    Mounts:     <none>
  Volumes:      <none>

測驗回滾到上一個版本：

$ kubectl rollout undo deployment nginx-1161 -n load-balance --to-revision=2
deployment.apps/nginx-1161 rolled back

$ kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   3         3         3       135m
nginx-1161-7cccdf449f   0         0         0       131m
nginx-1161-7d57d5c7c4   0         0         0       160m

如果不指定--to-revision，則默認回滾到上一個版本

$ kubectl rollout undo deployment nginx-1161 -n load-balance
deployment.apps/nginx-1161 rolled back

$ kubectl get rs -n load-balance
NAME                    DESIRED   CURRENT   READY   AGE
nginx-1161-56dd96d66c   0         0         0       138m
nginx-1161-7cccdf449f   3         3         3       135m
nginx-1161-7d57d5c7c4   0         0         0       164m

個人理解的回滾機制：

通過測驗發現，不帶 --to-revision 引數的 undo 回滾，會進入死回圈，如上圖所示，會始終在V2和V3版本之間來回的切換，而無法回滾到最早的 nginx-1161-7d57d5c7c4 版本，不知道這算不算K8S回滾機制存在的一個Bug呢？

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