Kubernetes 支持 postStart 和 preStop 事件。當一個主容器啟動后，Kubernetes 將立即發送 postStart 事件；在主容器被終結之前，Kubernetes 將發送一個 preStop 事件。
主機配置規划
| 服務器名稱(hostname) | 系統版本 | 配置 | 內網IP | 外網IP(模擬) |
|---|---|---|---|---|
| k8s-master | CentOS7.7 | 2C/4G/20G | 172.16.1.110 | 10.0.0.110 |
| k8s-node01 | CentOS7.7 | 2C/4G/20G | 172.16.1.111 | 10.0.0.111 |
| k8s-node02 | CentOS7.7 | 2C/4G/20G | 172.16.1.112 | 10.0.0.112 |
Pod容器生命周期
Pause容器說明
每個Pod里運行着一個特殊的被稱之為Pause的容器，其他容器則為業務容器，這些業務容器共享Pause容器的網絡棧和Volume掛載卷，因此他們之間通信和數據交換更為高效。在設計時可以充分利用這一特性，將一組密切相關的服務進程放入同一個Pod中；同一個Pod里的容器之間僅需通過localhost就能互相通信。
kubernetes中的pause容器主要為每個業務容器提供以下功能：
PID命名空間：Pod中的不同應用程序可以看到其他應用程序的進程ID。
網絡命名空間：Pod中的多個容器能夠訪問同一個IP和端口范圍。
IPC命名空間：Pod中的多個容器能夠使用SystemV IPC或POSIX消息隊列進行通信。
UTS命名空間：Pod中的多個容器共享一個主機名；Volumes（共享存儲卷）。
Pod中的各個容器可以訪問在Pod級別定義的Volumes。
主容器生命周期事件的處理函數
Kubernetes 支持 postStart 和 preStop 事件。當一個主容器啟動后，Kubernetes 將立即發送 postStart 事件；在主容器被終結之前，Kubernetes 將發送一個 preStop 事件。
postStart 和 preStop 處理函數示例
pod yaml文件
1 [root@k8s-master lifecycle]# pwd 2 /root/k8s_practice/lifecycle 3 [root@k8s-master lifecycle]# cat lifecycle-events.yaml 4 apiVersion: v1 5 kind: Pod 6 metadata: 7 name: lifecycle-demo-pod 8 namespace: default 9 labels: 10 test: lifecycle 11 spec: 12 containers: 13 - name: lifecycle-demo 14 image: registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17 15 imagePullPolicy: IfNotPresent 16 lifecycle: 17 postStart: 18 exec: 19 command: ["/bin/sh", "-c", "echo 'Hello from the postStart handler' >> /var/log/nginx/message"] 20 preStop: 21 exec: 22 command: ["/bin/sh", "-c", "echo 'Hello from the preStop handler' >> /var/log/nginx/message"] 23 volumeMounts: #定義容器掛載內容 24 - name: message-log #使用的存儲卷名稱，如果跟下面volume字段name值相同，則表示使用volume的nginx-site這個存儲卷 25 mountPath: /var/log/nginx/ #掛載至容器中哪個目錄 26 readOnly: false #讀寫掛載方式，默認為讀寫模式false 27 initContainers: 28 - name: init-myservice 29 image: registry.cn-beijing.aliyuncs.com/google_registry/busybox:1.24 30 command: ["/bin/sh", "-c", "echo 'Hello initContainers' >> /var/log/nginx/message"] 31 volumeMounts: #定義容器掛載內容 32 - name: message-log #使用的存儲卷名稱，如果跟下面volume字段name值相同，則表示使用volume的nginx-site這個存儲卷 33 mountPath: /var/log/nginx/ #掛載至容器中哪個目錄 34 readOnly: false #讀寫掛載方式，默認為讀寫模式false 35 volumes: #volumes字段定義了paues容器關聯的宿主機或分布式文件系統存儲卷 36 - name: message-log #存儲卷名稱 37 hostPath: #路徑，為宿主機存儲路徑 38 path: /data/volumes/nginx/log/ #在宿主機上目錄的路徑 39 type: DirectoryOrCreate #定義類型，這表示如果宿主機沒有此目錄則會自動創建
啟動pod，查看pod狀態
1 [root@k8s-master lifecycle]# kubectl apply -f lifecycle-events.yaml 2 pod/lifecycle-demo-pod created 3 [root@k8s-master lifecycle]# kubectl get pod -o wide 4 NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES 5 lifecycle-demo-pod 1/1 Running 0 5s 10.244.2.30 k8s-node02 <none> <none>
查看pod詳情
1 [root@k8s-master lifecycle]# kubectl describe pod lifecycle-demo-pod 2 Name: lifecycle-demo-pod 3 Namespace: default 4 Priority: 0 5 Node: k8s-node02/172.16.1.112 6 Start Time: Sat, 23 May 2020 22:08:04 +0800 7 Labels: test=lifecycle 8 ……………… 9 Init Containers: 10 init-myservice: 11 Container ID: docker://1cfabcb60b817efd5c7283ad9552dafada95dbe932f92822b814aaa9c38f8ba5 12 Image: registry.cn-beijing.aliyuncs.com/google_registry/busybox:1.24 13 Image ID: docker-pullable://registry.cn-beijing.aliyuncs.com/ducafe/busybox@sha256:f73ae051fae52945d92ee20d62c315306c593c59a429ccbbdcba4a488ee12269 14 Port: <none> 15 Host Port: <none> 16 Command: 17 /bin/sh 18 -c 19 echo 'Hello initContainers' >> /var/log/nginx/message 20 State: Terminated 21 Reason: Completed 22 Exit Code: 0 23 Started: Sat, 23 May 2020 22:08:06 +0800 24 Finished: Sat, 23 May 2020 22:08:06 +0800 25 Ready: True 26 Restart Count: 0 27 Environment: <none> 28 Mounts: 29 /var/log/nginx/ from message-log (rw) 30 /var/run/secrets/kubernetes.io/serviceaccount from default-token-v48g4 (ro) 31 Containers: 32 lifecycle-demo: 33 Container ID: docker://c07f7f3d838206878ad0bfeaec9b4222ac7d6b13fb758cc1b340ac43e7212a3a 34 Image: registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17 35 Image ID: docker-pullable://registry.cn-beijing.aliyuncs.com/google_registry/nginx@sha256:7ac7819e1523911399b798309025935a9968b277d86d50e5255465d6592c0266 36 Port: <none> 37 Host Port: <none> 38 State: Running 39 Started: Sat, 23 May 2020 22:08:07 +0800 40 Ready: True 41 Restart Count: 0 42 Environment: <none> 43 Mounts: 44 /var/log/nginx/ from message-log (rw) 45 /var/run/secrets/kubernetes.io/serviceaccount from default-token-v48g4 (ro) 46 Conditions: 47 Type Status 48 Initialized True 49 Ready True 50 ContainersReady True 51 PodScheduled True 52 Volumes: 53 message-log: 54 Type: HostPath (bare host directory volume) 55 Path: /data/volumes/nginx/log/ 56 HostPathType: DirectoryOrCreate 57 default-token-v48g4: 58 Type: Secret (a volume populated by a Secret) 59 SecretName: default-token-v48g4 60 Optional: false 61 QoS Class: BestEffort 62 Node-Selectors: <none> 63 Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s 64 node.kubernetes.io/unreachable:NoExecute for 300s 65 Events: 66 Type Reason Age From Message 67 ---- ------ ---- ---- ------- 68 Normal Scheduled <unknown> default-scheduler Successfully assigned default/lifecycle-demo-pod to k8s-node02 69 Normal Pulled 87s kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/busybox:1.24" already present on machine 70 Normal Created 87s kubelet, k8s-node02 Created container init-myservice 71 Normal Started 87s kubelet, k8s-node02 Started container init-myservice 72 Normal Pulled 86s kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17" already present on machine 73 Normal Created 86s kubelet, k8s-node02 Created container lifecycle-demo 74 Normal Started 86s kubelet, k8s-node02 Started container lifecycle-demo
此時在k8s-node02查看輸出信息如下：
1 [root@k8s-node02 log]# pwd 2 /data/volumes/nginx/log 3 [root@k8s-node02 log]# cat message 4 Hello initContainers 5 Hello from the postStart handler
由上可知，init Container先執行，然后當一個主容器啟動后，Kubernetes 將立即發送 postStart 事件。
停止該pod
1 [root@k8s-master lifecycle]# kubectl delete pod lifecycle-demo-pod 2 pod "lifecycle-demo-pod" deleted
此時在k8s-node02查看輸出信息如下：
1 [root@k8s-node02 log]# pwd 2 /data/volumes/nginx/log 3 [root@k8s-node02 log]# cat message 4 Hello initContainers 5 Hello from the postStart handler 6 Hello from the preStop handler
由上可知，當在容器被終結之前， Kubernetes 將發送一個 preStop 事件。
完畢！
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