Kubernetes 支持 postStart 和 preStop 事件。当一个主容器启动后,Kubernetes 将立即发送 postStart 事件;在主容器被终结之前,Kubernetes 将发送一个 preStop 事件。
服务器名称(hostname) | 系统版本 | 配置 | 内网IP | 外网IP(模拟) |
---|---|---|---|---|
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 |
每个Pod里运行着一个特殊的被称之为Pause的容器,其他容器则为业务容器,这些业务容器共享Pause容器的网络栈和Volume挂载卷,因此他们之间通信和数据交换更为高效。在设计时可以充分利用这一特性,将一组密切相关的服务进程放入同一个Pod中;同一个Pod里的容器之间仅需通过localhost就能互相通信。
kubernetes中的pause容器主要为每个业务容器提供以下功能:
PID命名空间:Pod中的不同应用程序可以看到其他应用程序的进程ID。
网络命名空间:Pod中的多个容器能够访问同一个IP和端口范围。
IPC命名空间:Pod中的多个容器能够使用SystemV IPC或POSIX消息队列进行通信。
UTS命名空间:Pod中的多个容器共享一个主机名;Volumes(共享存储卷)。
Pod中的各个容器可以访问在Pod级别定义的Volumes。
Kubernetes 支持 postStart 和 preStop 事件。当一个主容器启动后,Kubernetes 将立即发送 postStart 事件;在主容器被终结之前,Kubernetes 将发送一个 preStop 事件。
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: #定义容器挂载内容
24 - name: message-log #使用的存储卷名称,如果跟下面volume字段name值相同,则表示使用volume的nginx-site这个存储卷
25 mountPath: /var/log/nginx/ #挂载至容器中哪个目录
26 readOnly: false #读写挂载方式,默认为读写模式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: #定义容器挂载内容
32 - name: message-log #使用的存储卷名称,如果跟下面volume字段name值相同,则表示使用volume的nginx-site这个存储卷
33 mountPath: /var/log/nginx/ #挂载至容器中哪个目录
34 readOnly: false #读写挂载方式,默认为读写模式false
35 volumes: #volumes字段定义了paues容器关联的宿主机或分布式文件系统存储卷
36 - name: message-log #存储卷名称
37 hostPath: #路径,为宿主机存储路径
38 path: /data/volumes/nginx/log/ #在宿主机上目录的路径
39 type: DirectoryOrCreate #定义类型,这表示如果宿主机没有此目录则会自动创建
启动pod,查看pod状态
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详情
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
此时在k8s-node02查看输出信息如下:
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先执行,然后当一个主容器启动后,Kubernetes 将立即发送 postStart 事件。
停止该pod
1 [root@k8s-master lifecycle]# kubectl delete pod lifecycle-demo-pod
2 pod "lifecycle-demo-pod" deleted
此时在k8s-node02查看输出信息如下:
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,当在容器被终结之前, Kubernetes 将发送一个 preStop 事件。
完毕!
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