k8s中的pod更新策略

StatefulSet（有狀態集，縮寫為sts）常用於部署有狀態的且需要有序啟動的應用程序，比如在進行SpringCloud項目容器化時，Eureka的部署是比較適合用StatefulSet部署方式的，可以給每個Eureka實例創建一個唯一且固定的標識符，並且每個Eureka實例無需配置多余的Service，其余Spring Boot應用可以直接通過Eureka的Headless Service即可進行注冊。
Eureka的statefulset的資源名稱是
eureka，eureka-0
        eureka-1
        eureka-2
Service：headless service，沒有ClusterIP [每個]	
eureka-svc Eureka-0.eureka-svc.NAMESPACE_NAME  eureka-1.eureka-svc …
連接 eureka的資源名稱為：eureka

statefullset示例

apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
          name: web


[root@k8s-master01 statefullset]# kubectl create -f statefullset.yaml
service/nginx created
statefulset.apps/web created



#擴容：
replicas: 2  #[定義副本集數量]

[root@k8s-master01 statefullset]# kubectl get pod
web-0                    1/1     Running   0          1m
web-1                    1/1     Running   0          1m


#命令擴容
[root@k8s-master01 statefullset]# kubectl scale --replicas=3 sts web
statefulset.apps/web scaled


#檢查擴容
[root@k8s-master01 statefullset]# kubectl get pod
NAME                     READY   STATUS    RESTARTS   AGE
web-0                    1/1     Running   0          15m
web-1                    1/1     Running   0          12m
web-2                    1/1     Running   0          35s



#檢查擴容流程：
[root@k8s-master01 ~]# kubectl scale --replicas=5 sts web
statefulset.apps/web scaled

[root@k8s-master01 ~]# kubectl get pod -l app=nginx -w
NAME                     READY   STATUS    RESTARTS   AGE
nginx-68db656dd8-cc4jv   1/1     Running   0          36h
nginx-68db656dd8-hvj8x   1/1     Running   0          36h
web-0                    1/1     Running   0          18h
web-1                    1/1     Running   0          18h
web-2                    0/1     Pending   0          0s
web-2                    0/1     Pending   0          0s
web-2                    0/1     ContainerCreating   0          0s
web-2                    1/1     Running             0          18s
web-3                    0/1     Pending             0          0s
web-3                    0/1     Pending             0          0s
web-3                    0/1     ContainerCreating   0          0s
web-3                    1/1     Running             0          18s
web-4                    0/1     Pending             0          0s
web-4                    0/1     Pending             0          0s
web-4                    0/1     ContainerCreating   0          0s
web-4                    1/1     Running             0          17s

statefulset 更新策略

#默認更新策略：
  updateStrategy:
    rollingUpdate:
      partition: 0         # 設置為1 一次更新一個，如果設置為 0  則是隨機更新
    type: RollingUpdate    #--- statefulset默認更新策略 滾動更新，有一個更新失敗就不會繼續更新，deployment是隨機更新模式
    

statefulset更新策略： 
  1. RollingUpdate  滾動更新 [從下往上更新，倒序更新]
  2. OnDelete       手動更新 [需要刪除一個pod才會觸發更新策略]

默認更新策略RollingUpdate示例：

 執行命令: kubectl edit sts web
 找到:
 containers:
   - image: nginx
 改為:
  containers:
   - image: nginx:1.15.2
   
   
   
 # 查看更新過程：
 [root@k8s-master01 ~]# kubectl get pod -l app=nginx -w 
NAME                     READY   STATUS              RESTARTS   AGE
web-0                    1/1     Running             0          20h
web-1                    1/1     Running             0          20h
web-2                    1/1     Running             0          89m
web-2                    1/1     Terminating         0          90m
web-2                    0/1     Terminating         0          90m
web-2                    0/1     Terminating         0          90m
web-2                    0/1     Terminating         0          90m
web-2                    0/1     Pending             0          0s
web-2                    0/1     Pending             0          0s
web-2                    0/1     ContainerCreating   0          0s
web-2                    1/1     Running             0          19s
web-1                    1/1     Terminating         0          20h
web-1                    0/1     Terminating         0          20h
web-1                    0/1     Terminating         0          20h
web-1                    0/1     Terminating         0          20h
web-1                    0/1     Pending             0          0s
web-1                    0/1     Pending             0          0s
web-1                    0/1     ContainerCreating   0          0s
web-1                    1/1     Running             0          20s
web-0                    1/1     Terminating         0          20h
web-0                    0/1     Terminating         0          20h
web-0                    0/1     Terminating         0          20h
web-0                    0/1     Terminating         0          20h
web-0                    0/1     Pending             0          0s
web-0                    0/1     Pending             0          0s
web-0                    0/1     ContainerCreating   0          0s
web-0                    1/1     Running             0          19s

 # 查看更新結果：
[root@k8s-master01 ~]# kubectl get pod -l app=nginx
NAME                     READY   STATUS    RESTARTS   AGE
web-0                    1/1     Running   0          59s
web-1                    1/1     Running   0          88s
web-2                    1/1     Running   0          118s

# 驗證結果：
[root@k8s-master01 ~]# kubectl exec -it web-0 -- sh
# nginx -v
nginx version: nginx/1.15.2

OnDelete策略示例：

# 修改為 OnDelete 策略
# kubectl edit sts web

找到: 
updateStrategy:
  rollingUpdate:
    partition: 0
  type: RollingUpdate
  
改為:     
 updateStrategy:
   type: OnDelete

# 修改鏡像版本來查看 是否此策略會更新版本
image: nginx
#改為：
image: nginx:1.15.3

#保存 [刪除 rollingUpdate: 與 partition: 0 並且將 type: RollingUpdate 改為 type: OnDelete ]


#檢查：
[root@k8s-master01 ~]# kubectl get pod |grep web
NAME                     READY   STATUS    RESTARTS   AGE
web-0                    1/1     Running   0          6m58s
web-1                    1/1     Running   0          7m17s  # <-- 並未更新
web-2                    1/1     Running   0          7m48s    

#再次修改鏡像版本並刪除其中一個pod：
[root@k8s-master01 ~]# kubectl edit sts web   #把 nginx:1.15.3 改為 nginx:1.15.2
statefulset.apps/web edited
[root@k8s-master01 statefullset]# kubectl delete pod web-1 
pod "web-1" deleted

# 檢查刪除的pod更新狀態：
[root@k8s-master01 statefullset]# kubectl get pod web-1 -o yaml|grep image
  - image: nginx:1.15.3
    imagePullPolicy: Always
    image: nginx:1.15.3
    imageID: docker-pullable://nginx@sha256:24a0c4b4a4c0eb97a1aabb8e29f18e917d05abfe1b7a7c07857230879ce7d3d3


# 檢查未刪除的pod版本：
[root@k8s-master01 statefullset]# kubectl get pod web-0 -o yaml|grep image
  - image: nginx
    imagePullPolicy: Always
    image: nginx:latest
    imageID: docker-pullable://nginx@sha256:353c20f74d9b6aee359f30e8e4f69c3d7eaea2f610681c4a95849a2fd7c497f9
    
# 再刪除這個未刪除的版本檢查刪除后是否會更新，剛刪除的web-1 現在刪除web-0：
[root@k8s-master01 statefullset]# kubectl delete pod web-0 
pod "web-0" deleted

#檢查刪除后的web-0 是否更新了版本
[root@k8s-master01 statefullset]# kubectl get pod web-0 -o yaml|grep image
  - image: nginx:1.15.3
    imagePullPolicy: Always
    image: nginx:1.15.3    # -- 確定已經更新了版本
    imageID: docker-pullable://nginx@sha256:24a0c4b4a4c0eb97a1aabb8e29f18e917d05abfe1b7a7c07857230879ce7d3d3
    
    
這就是Ondelete的更新策略