K8S中Pod的生命周期与ExecAction、TCPSocketAction和HTTPGetAction探针检测
主机配置规划
| 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 |
Pod容器生命周期
Pause容器说明
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。
容器探针
探针是由 kubelet 对容器执行的定期诊断。要执行诊断，则需kubelet 调用由容器实现的 Handler。探针有三种类型的处理程序：
- ExecAction：在容器内执行指定命令。如果命令退出时返回码为 0 则认为诊断成功。
- CPSocketAction：对指定端口上的容器的 IP 地址进行 TCP 检查。如果端口打开，则诊断被认为是成功的。
- HTTPGetAction：对指定的端口和路径上的容器的 IP 地址执行 HTTP Get 请求。如果响应的状态码大于等于200 且小于 400，则诊断被认为是成功的。
每次探测都将获得以下三种结果之一：
- 成功：容器通过了诊断。
- 失败：容器未通过诊断。
- 未知：诊断失败，因此不会采取任何行动。
Kubelet 可以选择是否在容器上运行三种探针执行和做出反应：
- livenessProbe：指示容器是否正在运行。如果存活探测失败，则 kubelet 会杀死容器，并且容器将受到其重启策略的影响。如果容器不提供存活探针，则默认状态为 Success。
- readinessProbe：指示容器是否准备好服务请求【对外接受请求访问】。如果就绪探测失败，端点控制器将从与 Pod 匹配的所有 Service 的端点中删除该 Pod 的 IP 地址。初始延迟之前的就绪状态默认为 Failure。如果容器不提供就绪探针，则默认状态为 Success。
- startupProbe: 指示容器中的应用是否已经启动。如果提供了启动探测(startup probe)，则禁用所有其他探测，直到它成功为止。如果启动探测失败，kubelet 将杀死容器，容器服从其重启策略进行重启。如果容器没有提供启动探测，则默认状态为成功Success。
备注：可以以Tomcat web服务为例。
容器重启策略
PodSpec 中有一个 restartPolicy 字段，可能的值为 Always、OnFailure 和 Never。默认为 Always。
Always表示一旦不管以何种方式终止运行，kubelet都将重启；OnFailure表示只有Pod以非0退出码退出才重启；Nerver表示不再重启该Pod。
restartPolicy 适用于 Pod 中的所有容器。restartPolicy 仅指通过同一节点上的 kubelet 重新启动容器。失败的容器由 kubelet 以五分钟为上限的指数退避延迟（10秒，20秒，40秒…）重新启动，并在成功执行十分钟后重置。如 Pod 文档中所述，一旦pod绑定到一个节点，Pod 将永远不会重新绑定到另一个节点。
存活（liveness）和就绪（readiness）探针的使用场景
如果容器中的进程能够在遇到问题或不健康的情况下自行崩溃，则不一定需要存活探针；kubelet 将根据 Pod 的restartPolicy 自动执行正确的操作。
如果你希望容器在探测失败时被杀死并重新启动，那么请指定一个存活探针，并指定restartPolicy 为 Always 或 OnFailure。
如果要仅在探测成功时才开始向 Pod 发送流量，请指定就绪探针。在这种情况下，就绪探针可能与存活探针相同，但是 spec 中的就绪探针的存在意味着 Pod 将在没有接收到任何流量的情况下启动，并且只有在探针探测成功后才开始接收流量。
Pod phase（阶段）
Pod 的 status 定义在 PodStatus 对象中，其中有一个 phase 字段。
Pod 的运行阶段（phase）是 Pod 在其生命周期中的简单宏观概述。该阶段并不是对容器或 Pod 的综合汇总，也不是为了做为综合状态机。
Pod 相位的数量和含义是严格指定的。除了本文档中列举的内容外，不应该再假定 Pod 有其他的 phase 值。
下面是 phase 可能的值：
- 挂起（Pending）：Pod 已被 Kubernetes 系统接受，但有一个或者多个容器镜像尚未创建。等待时间包括调度 Pod 的时间和通过网络下载镜像的时间，这可能需要花点时间。
- 运行中（Running）：该 Pod 已经绑定到了一个节点上，Pod 中所有的容器都已被创建。至少有一个容器正在运行，或者正处于启动或重启状态。
- 成功（Succeeded）：Pod 中的所有容器都被成功终止，并且不会再重启。
- 失败（Failed）：Pod 中的所有容器都已终止了，并且至少有一个容器是因为失败终止。也就是说，容器以非0状态退出或者被系统终止。
- 未知（Unknown）：因为某些原因无法取得 Pod 的状态，通常是因为与 Pod 所在主机通信失败。
检测探针-就绪检测
pod yaml脚本
1 [root@k8s-master lifecycle]# pwd 2 /root/k8s_practice/lifecycle 3 [root@k8s-master lifecycle]# cat readinessProbe-httpget.yaml 4 apiVersion: v1 5 kind: Pod 6 metadata: 7 name: readiness-httpdget-pod 8 namespace: default 9 labels: 10 test: readiness-httpdget 11 spec: 12 containers: 13 - name: readiness-httpget 14 image: registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17 15 imagePullPolicy: IfNotPresent 16 readinessProbe: 17 httpGet: 18 path: /index1.html 19 port: 80 20 initialDelaySeconds: 5 #容器启动完成后，kubelet在执行第一次探测前应该等待 5 秒。默认是 0 秒，最小值是 0。 21 periodSeconds: 3 #指定 kubelet 每隔 3 秒执行一次存活探测。默认是 10 秒。最小值是 1
创建 Pod，并查看pod状态
1 [root@k8s-master lifecycle]# kubectl apply -f readinessProbe-httpget.yaml 2 pod/readiness-httpdget-pod created 3 [root@k8s-master lifecycle]# kubectl get pod -n default -o wide 4 NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES 5 readiness-httpdget-pod 0/1 Running 0 5s 10.244.2.25 k8s-node02 <none> <none>
查看pod详情
1 [root@k8s-master lifecycle]# kubectl describe pod readiness-httpdget-pod
2 Name: readiness-httpdget-pod
3 Namespace: default
4 Priority: 0
5 Node: k8s-node02/172.16.1.112
6 Start Time: Sat, 23 May 2020 16:10:04 +0800
7 Labels: test=readiness-httpdget
8 Annotations: kubectl.kubernetes.io/last-applied-configuration:
9 {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"labels":{"test":"readiness-httpdget"},"name":"readiness-httpdget-pod","names...
10 Status: Running
11 IP: 10.244.2.25
12 IPs:
13 IP: 10.244.2.25
14 Containers:
15 readiness-httpget:
16 Container ID: docker://066d66aaef191b1db08e1b3efba6a9be75378d2fe70e99400fc513b91242089c
17 ………………
18 Port: <none>
19 Host Port: <none>
20 State: Running
21 Started: Sat, 23 May 2020 16:10:05 +0800
22 Ready: False ##### 状态为False
23 Restart Count: 0
24 Readiness: http-get http://:80/index1.html delay=5s timeout=1s period=3s #success=1 #failure=3
25 Environment: <none>
26 Mounts:
27 /var/run/secrets/kubernetes.io/serviceaccount from default-token-v48g4 (ro)
28 Conditions:
29 Type Status
30 Initialized True
31 Ready False ##### 为False
32 ContainersReady False ##### 为False
33 PodScheduled True
34 Volumes:
35 default-token-v48g4:
36 Type: Secret (a volume populated by a Secret)
37 SecretName: default-token-v48g4
38 Optional: false
39 QoS Class: BestEffort
40 Node-Selectors: <none>
41 Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
42 node.kubernetes.io/unreachable:NoExecute for 300s
43 Events:
44 Type Reason Age From Message
45 ---- ------ ---- ---- -------
46 Normal Scheduled <unknown> default-scheduler Successfully assigned default/readiness-httpdget-pod to k8s-node02
47 Normal Pulled 49s kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17" already present on machine
48 Normal Created 49s kubelet, k8s-node02 Created container readiness-httpget
49 Normal Started 49s kubelet, k8s-node02 Started container readiness-httpget
50 Warning Unhealthy 2s (x15 over 44s) kubelet, k8s-node02 Readiness probe failed: HTTP probe failed with statuscode: 404
由上可见，容器未就绪。
我们进入pod的第一个容器，然后创建对应的文件
1 [root@k8s-master lifecycle]# kubectl exec -it readiness-httpdget-pod -c readiness-httpget bash 2 root@readiness-httpdget-pod:/# cd /usr/share/nginx/html 3 root@readiness-httpdget-pod:/usr/share/nginx/html# ls 4 50x.html index.html 5 root@readiness-httpdget-pod:/usr/share/nginx/html# echo "readiness-httpdget info" > index1.html 6 root@readiness-httpdget-pod:/usr/share/nginx/html# ls 7 50x.html index.html index1.html
之后看pod状态与详情
1 [root@k8s-master lifecycle]# kubectl get pod -n default -o wide
2 NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
3 readiness-httpdget-pod 1/1 Running 0 2m30s 10.244.2.25 k8s-node02 <none> <none>
4 [root@k8s-master lifecycle]# kubectl describe pod readiness-httpdget-pod
5 Name: readiness-httpdget-pod
6 Namespace: default
7 Priority: 0
8 Node: k8s-node02/172.16.1.112
9 Start Time: Sat, 23 May 2020 16:10:04 +0800
10 Labels: test=readiness-httpdget
11 Annotations: kubectl.kubernetes.io/last-applied-configuration:
12 {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"labels":{"test":"readiness-httpdget"},"name":"readiness-httpdget-pod","names...
13 Status: Running
14 IP: 10.244.2.25
15 IPs:
16 IP: 10.244.2.25
17 Containers:
18 readiness-httpget:
19 Container ID: docker://066d66aaef191b1db08e1b3efba6a9be75378d2fe70e99400fc513b91242089c
20 ………………
21 Port: <none>
22 Host Port: <none>
23 State: Running
24 Started: Sat, 23 May 2020 16:10:05 +0800
25 Ready: True ##### 状态为True
26 Restart Count: 0
27 Readiness: http-get http://:80/index1.html delay=5s timeout=1s period=3s #success=1 #failure=3
28 Environment: <none>
29 Mounts:
30 /var/run/secrets/kubernetes.io/serviceaccount from default-token-v48g4 (ro)
31 Conditions:
32 Type Status
33 Initialized True
34 Ready True ##### 为True
35 ContainersReady True ##### 为True
36 PodScheduled True
37 Volumes:
38 default-token-v48g4:
39 Type: Secret (a volume populated by a Secret)
40 SecretName: default-token-v48g4
41 Optional: false
42 QoS Class: BestEffort
43 Node-Selectors: <none>
44 Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
45 node.kubernetes.io/unreachable:NoExecute for 300s
46 Events:
47 Type Reason Age From Message
48 ---- ------ ---- ---- -------
49 Normal Scheduled <unknown> default-scheduler Successfully assigned default/readiness-httpdget-pod to k8s-node02
50 Normal Pulled 2m33s kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17" already present on machine
51 Normal Created 2m33s kubelet, k8s-node02 Created container readiness-httpget
52 Normal Started 2m33s kubelet, k8s-node02 Started container readiness-httpget
53 Warning Unhealthy 85s (x22 over 2m28s) kubelet, k8s-node02 Readiness probe failed: HTTP probe failed with statuscode: 404
由上可见，容器已就绪。
检测探针-存活检测
存活检测-执行命令
pod yaml脚本
1 [root@k8s-master lifecycle]# pwd 2 /root/k8s_practice/lifecycle 3 [root@k8s-master lifecycle]# cat livenessProbe-exec.yaml 4 apiVersion: v1 5 kind: Pod 6 metadata: 7 name: liveness-exec-pod 8 labels: 9 test: liveness 10 spec: 11 containers: 12 - name: liveness-exec 13 image: registry.cn-beijing.aliyuncs.com/google_registry/busybox:1.24 14 imagePullPolicy: IfNotPresent 15 args: 16 - /bin/sh 17 - -c 18 - touch /tmp/healthy; sleep 30; rm -rf /tmp/healthy; sleep 600 19 livenessProbe: 20 exec: 21 command: 22 - cat 23 - /tmp/healthy 24 initialDelaySeconds: 5 # 第一次检测前等待5秒 25 periodSeconds: 3 # 检测周期3秒一次
这个容器生命的前 30 秒，/tmp/healthy 文件是存在的。所以在这最开始的 30 秒内，执行命令 cat /tmp/healthy 会返回成功码。30 秒之后，执行命令 cat /tmp/healthy 就会返回失败状态码。
创建 Pod
1 [root@k8s-master lifecycle]# kubectl apply -f livenessProbe-exec.yaml 2 pod/liveness-exec-pod created
在 30 秒内，查看 Pod 的描述：
1 [root@k8s-master lifecycle]# kubectl get pod -o wide 2 NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES 3 liveness-exec-pod 1/1 Running 0 17s 10.244.2.21 k8s-node02 <none> <none> 4 [root@k8s-master lifecycle]# kubectl describe pod liveness-exec-pod 5 Name: liveness-exec-pod 6 Namespace: default 7 Priority: 0 8 Node: k8s-node02/172.16.1.112 9 ……………… 10 Events: 11 Type Reason Age From Message 12 ---- ------ ---- ---- ------- 13 Normal Scheduled 25s default-scheduler Successfully assigned default/liveness-exec-pod to k8s-node02 14 Normal Pulled 24s kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/busybox:1.24" already present on machine 15 Normal Created 24s kubelet, k8s-node02 Created container liveness-exec 16 Normal Started 24s kubelet, k8s-node02 Started container liveness-exec
输出结果显示：存活探测器成功。
35 秒之后，再来看 Pod 的描述：
1 [root@k8s-master lifecycle]# kubectl get pod -o wide # 显示 RESTARTS 的值增加了 1 2 NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES 3 liveness-exec-pod 1/1 Running 1 89s 10.244.2.22 k8s-node02 <none> <none> 4 [root@k8s-master lifecycle]# kubectl describe pod liveness-exec-pod 5 ……………… 6 Events: 7 Type Reason Age From Message 8 ---- ------ ---- ---- ------- 9 Normal Scheduled 42s default-scheduler Successfully assigned default/liveness-exec-pod to k8s-node02 10 Normal Pulled 41s kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/busybox:1.24" already present on machine 11 Normal Created 41s kubelet, k8s-node02 Created container liveness-exec 12 Normal Started 41s kubelet, k8s-node02 Started container liveness-exec 13 Warning Unhealthy 2s (x3 over 8s) kubelet, k8s-node02 Liveness probe failed: cat: can't open '/tmp/healthy': No such file or directory 14 Normal Killing 2s kubelet, k8s-node02 Container liveness-exec failed liveness probe, will be restarted
由上可见，在输出结果的最下面，有信息显示存活探测器失败了，因此这个容器被杀死并且被重建了。
存活检测-HTTP请求
pod yaml脚本
1 [root@k8s-master lifecycle]# pwd 2 /root/k8s_practice/lifecycle 3 [root@k8s-master lifecycle]# cat livenessProbe-httpget.yaml 4 apiVersion: v1 5 kind: Pod 6 metadata: 7 name: liveness-httpget-pod 8 labels: 9 test: liveness 10 spec: 11 containers: 12 - name: liveness-httpget 13 image: registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17 14 imagePullPolicy: IfNotPresent 15 ports: 16 - name: http 17 containerPort: 80 18 livenessProbe: 19 httpGet: # 任何大于或等于 200 并且小于 400 的返回码表示成功，其它返回码都表示失败。 20 path: /index.html 21 port: 80 22 httpHeaders: #请求中自定义的 HTTP 头。HTTP 头字段允许重复。 23 - name: Custom-Header 24 value: Awesome 25 initialDelaySeconds: 5 26 periodSeconds: 3
创建 Pod，查看pod状态
1 [root@k8s-master lifecycle]# kubectl apply -f livenessProbe-httpget.yaml 2 pod/liveness-httpget-pod created 3 [root@k8s-master lifecycle]# kubectl get pod -n default -o wide 4 NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES 5 liveness-httpget-pod 1/1 Running 0 3s 10.244.2.27 k8s-node02 <none> <none>
查看pod详情
1 [root@k8s-master lifecycle]# kubectl describe pod liveness-httpget-pod
2 Name: liveness-httpget-pod
3 Namespace: default
4 Priority: 0
5 Node: k8s-node02/172.16.1.112
6 Start Time: Sat, 23 May 2020 16:45:25 +0800
7 Labels: test=liveness
8 Annotations: kubectl.kubernetes.io/last-applied-configuration:
9 {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"labels":{"test":"liveness"},"name":"liveness-httpget-pod","namespace":"defau...
10 Status: Running
11 IP: 10.244.2.27
12 IPs:
13 IP: 10.244.2.27
14 Containers:
15 liveness-httpget:
16 Container ID: docker://4b42a351414667000fe94d4f3166d75e72a3401e549fed723126d2297124ea1a
17 ………………
18 Port: 80/TCP
19 Host Port: 8080/TCP
20 State: Running
21 Started: Sat, 23 May 2020 16:45:26 +0800
22 Ready: True
23 Restart Count: 0
24 Liveness: http-get http://:80/index.html delay=5s timeout=1s period=3s #success=1 #failure=3
25 Environment: <none>
26 Mounts:
27 /var/run/secrets/kubernetes.io/serviceaccount from default-token-v48g4 (ro)
28 Conditions:
29 Type Status
30 Initialized True
31 Ready True
32 ContainersReady True
33 PodScheduled True
34 ………………
35 Events:
36 Type Reason Age From Message
37 ---- ------ ---- ---- -------
38 Normal Scheduled <unknown> default-scheduler Successfully assigned default/liveness-httpget-pod to k8s-node02
39 Normal Pulled 5m52s kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17" already present on machine
40 Normal Created 5m52s kubelet, k8s-node02 Created container liveness-httpget
41 Normal Started 5m52s kubelet, k8s-node02 Started container liveness-httpget
由上可见，pod存活检测正常
我们进入pod的第一个容器，然后删除对应的文件
1 [root@k8s-master lifecycle]# kubectl exec -it liveness-httpget-pod -c liveness-httpget bash 2 root@liveness-httpget-pod:/# cd /usr/share/nginx/html/ 3 root@liveness-httpget-pod:/usr/share/nginx/html# ls 4 50x.html index.html 5 root@liveness-httpget-pod:/usr/share/nginx/html# rm -f index.html 6 root@liveness-httpget-pod:/usr/share/nginx/html# ls 7 50x.html
再次看pod状态和详情，可见Pod的RESTARTS从0变为了1。
1 [root@k8s-master lifecycle]# kubectl get pod -n default -o wide # RESTARTS 从0变为了1
2 NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
3 liveness-httpget-pod 1/1 Running 1 8m16s 10.244.2.27 k8s-node02 <none> <none>
4 [root@k8s-master lifecycle]# kubectl describe pod liveness-httpget-pod
5 Name: liveness-httpget-pod
6 Namespace: default
7 Priority: 0
8 Node: k8s-node02/172.16.1.112
9 Start Time: Sat, 23 May 2020 16:45:25 +0800
10 Labels: test=liveness
11 Annotations: kubectl.kubernetes.io/last-applied-configuration:
12 {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"labels":{"test":"liveness"},"name":"liveness-httpget-pod","namespace":"defau...
13 Status: Running
14 IP: 10.244.2.27
15 IPs:
16 IP: 10.244.2.27
17 Containers:
18 liveness-httpget:
19 Container ID: docker://5d0962d383b1df5e59cd3d1100b259ff0415ac37c8293b17944034f530fb51c8
20 ………………
21 Port: 80/TCP
22 Host Port: 8080/TCP
23 State: Running
24 Started: Sat, 23 May 2020 16:53:38 +0800
25 Last State: Terminated
26 Reason: Completed
27 Exit Code: 0
28 Started: Sat, 23 May 2020 16:45:26 +0800
29 Finished: Sat, 23 May 2020 16:53:38 +0800
30 Ready: True
31 Restart Count: 1
32 Liveness: http-get http://:80/index.html delay=5s timeout=1s period=3s #success=1 #failure=3
33 Environment: <none>
34 Mounts:
35 /var/run/secrets/kubernetes.io/serviceaccount from default-token-v48g4 (ro)
36 Conditions:
37 Type Status
38 Initialized True
39 Ready True
40 ContainersReady True
41 PodScheduled True
42 Volumes:
43 default-token-v48g4:
44 Type: Secret (a volume populated by a Secret)
45 SecretName: default-token-v48g4
46 Optional: false
47 QoS Class: BestEffort
48 Node-Selectors: <none>
49 Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
50 node.kubernetes.io/unreachable:NoExecute for 300s
51 Events:
52 Type Reason Age From Message
53 ---- ------ ---- ---- -------
54 Normal Scheduled <unknown> default-scheduler Successfully assigned default/liveness-httpget-pod to k8s-node02
55 Normal Pulled 7s (x2 over 8m19s) kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17" already present on machine
56 Normal Created 7s (x2 over 8m19s) kubelet, k8s-node02 Created container liveness-httpget
57 Normal Started 7s (x2 over 8m19s) kubelet, k8s-node02 Started container liveness-httpget
58 Warning Unhealthy 7s (x3 over 13s) kubelet, k8s-node02 Liveness probe failed: HTTP probe failed with statuscode: 404
59 Normal Killing 7s kubelet, k8s-node02 Container liveness-httpget failed liveness probe, will be restarted
由上可见，当liveness-httpget检测失败，重建了Pod容器
存活检测-TCP端口
pod yaml脚本
1 [root@k8s-master lifecycle]# pwd 2 /root/k8s_practice/lifecycle 3 [root@k8s-master lifecycle]# cat livenessProbe-tcp.yaml 4 apiVersion: v1 5 kind: Pod 6 metadata: 7 name: liveness-tcp-pod 8 labels: 9 test: liveness 10 spec: 11 containers: 12 - name: liveness-tcp 13 image: registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17 14 imagePullPolicy: IfNotPresent 15 ports: 16 - name: http 17 containerPort: 80 18 livenessProbe: 19 tcpSocket: 20 port: 80 21 initialDelaySeconds: 5 22 periodSeconds: 3
TCP探测正常情况
创建 Pod，查看pod状态
1 [root@k8s-master lifecycle]# kubectl apply -f livenessProbe-tcp.yaml 2 pod/liveness-tcp-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 liveness-tcp-pod 1/1 Running 0 50s 10.244.4.23 k8s-node01 <none> <none>
查看pod详情
1 [root@k8s-master lifecycle]# kubectl describe pod liveness-tcp-pod
2 Name: liveness-tcp-pod
3 Namespace: default
4 Priority: 0
5 Node: k8s-node01/172.16.1.111
6 Start Time: Sat, 23 May 2020 18:02:46 +0800
7 Labels: test=liveness
8 Annotations: kubectl.kubernetes.io/last-applied-configuration:
9 {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"labels":{"test":"liveness"},"name":"liveness-tcp-pod","namespace":"default"}...
10 Status: Running
11 IP: 10.244.4.23
12 IPs:
13 IP: 10.244.4.23
14 Containers:
15 liveness-tcp:
16 Container ID: docker://4de13e7c2e36c028b2094bf9dcf8e2824bfd15b8c45a0b963e301b91ee1a926d
17 ………………
18 Port: 80/TCP
19 Host Port: 8080/TCP
20 State: Running
21 Started: Sat, 23 May 2020 18:03:04 +0800
22 Ready: True
23 Restart Count: 0
24 Liveness: tcp-socket :80 delay=5s timeout=1s period=3s #success=1 #failure=3
25 Environment: <none>
26 Mounts:
27 /var/run/secrets/kubernetes.io/serviceaccount from default-token-v48g4 (ro)
28 Conditions:
29 Type Status
30 Initialized True
31 Ready True
32 ContainersReady True
33 PodScheduled True
34 Volumes:
35 default-token-v48g4:
36 Type: Secret (a volume populated by a Secret)
37 SecretName: default-token-v48g4
38 Optional: false
39 QoS Class: BestEffort
40 Node-Selectors: <none>
41 Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
42 node.kubernetes.io/unreachable:NoExecute for 300s
43 Events:
44 Type Reason Age From Message
45 ---- ------ ---- ---- -------
46 Normal Scheduled <unknown> default-scheduler Successfully assigned default/liveness-tcp-pod to k8s-node01
47 Normal Pulling 74s kubelet, k8s-node01 Pulling image "registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17"
48 Normal Pulled 58s kubelet, k8s-node01 Successfully pulled image "registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17"
49 Normal Created 57s kubelet, k8s-node01 Created container liveness-tcp
50 Normal Started 57s kubelet, k8s-node01 Started container liveness-tcp
以上是正常情况，可见存活探测成功。
模拟TCP探测失败情况
将上面yaml文件中的探测TCP端口进行如下修改：
1 livenessProbe: 2 tcpSocket: 3 port: 8090 # 之前是80
删除之前的pod并重新创建，并过一会儿看pod状态
1 [root@k8s-master lifecycle]# kubectl apply -f livenessProbe-tcp.yaml 2 pod/liveness-tcp-pod created 3 [root@k8s-master lifecycle]# kubectl get pod -o wide # 可见RESTARTS变为了1，再过一会儿会变为2，之后依次叠加 4 NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES 5 liveness-tcp-pod 1/1 Running 1 25s 10.244.2.28 k8s-node02 <none> <none>
pod详情
1 [root@k8s-master lifecycle]# kubectl describe pod liveness-tcp-pod 2 Name: liveness-tcp-pod 3 Namespace: default 4 Priority: 0 5 Node: k8s-node02/172.16.1.112 6 Start Time: Sat, 23 May 2020 18:08:32 +0800 7 Labels: test=liveness 8 ……………… 9 Events: 10 Type Reason Age From Message 11 ---- ------ ---- ---- ------- 12 Normal Scheduled <unknown> default-scheduler Successfully assigned default/liveness-tcp-pod to k8s-node02 13 Normal Pulled 12s (x2 over 29s) kubelet, k8s-node02 Container image "registry.cn-beijing.aliyuncs.com/google_registry/nginx:1.17" already present on machine 14 Normal Created 12s (x2 over 29s) kubelet, k8s-node02 Created container liveness-tcp 15 Normal Started 12s (x2 over 28s) kubelet, k8s-node02 Started container liveness-tcp 16 Normal Killing 12s kubelet, k8s-node02 Container liveness-tcp failed liveness probe, will be restarted 17 Warning Unhealthy 0s (x4 over 18s) kubelet, k8s-node02 Liveness probe failed: dial tcp 10.244.2.28:8090: connect: connection refused
由上可见，liveness-tcp检测失败，重建了Pod容器。
检测探针-启动检测
有时候，会有一些现有的应用程序在启动时需要较多的初始化时间【如：Tomcat服务】。这种情况下，在不影响对触发这种探测的死锁的快速响应的情况下，设置存活探测参数是要有技巧的。
技巧就是使用一个命令来设置启动探测。针对HTTP 或者 TCP 检测，可以通过设置 failureThreshold * periodSeconds 参数来保证有足够长的时间应对糟糕情况下的启动时间。
示例如下：
pod yaml文件
1 [root@k8s-master lifecycle]# pwd 2 /root/k8s_practice/lifecycle 3 [root@k8s-master lifecycle]# cat startupProbe-httpget.yaml 4 apiVersion: v1 5 kind: Pod 6 metadata: 7 name: startup-pod 8 labels: 9 test: startup 10 spec: 11 containers: 12 - name: startup 13 image: registry.cn-beijing.aliyuncs.com/google_registry/tomcat:7.0.94-jdk8-openjdk 14 imagePullPolicy: IfNotPresent 15 ports: 16 - name: web-port 17 containerPort: 8080 18 hostPort: 8080 19 livenessProbe: 20 httpGet: 21 path: /index.jsp 22 port: web-port 23 initialDelaySeconds: 5 24 periodSeconds: 10 25 failureThreshold: 1 26 startupProbe: 27 httpGet: 28 path: /index.jsp 29 port: web-port 30 periodSeconds: 10 #指定 kubelet 每隔 10 秒执行一次存活探测。默认是 10 秒。最小值是 1 31 failureThreshold: 30 #最大的失败次数
启动pod，并查看状态
1 [root@k8s-master lifecycle]# kubectl apply -f startupProbe-httpget.yaml 2 pod/startup-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 startup-pod 1/1 Running 0 8m46s 10.244.4.26 k8s-node01 <none> <none>
查看pod详情
[root@k8s-master ~]# kubectl describe pod startup-pod
有启动探测，应用程序将会有最多 5 分钟(30 * 10 = 300s) 的时间来完成它的启动。一旦启动探测成功一次，存活探测任务就会接管对容器的探测，对容器死锁可以快速响应。 如果启动探测一直没有成功，容器会在 300 秒后被杀死，并且根据 restartPolicy 来设置 Pod 状态。
探测器配置详解
使用如下这些字段可以精确的控制存活和就绪检测行为：
- initialDelaySeconds：容器启动后要等待多少秒后存活和就绪探测器才被初始化，默认是 0 秒，最小值是 0。
- periodSeconds：执行探测的时间间隔（单位是秒）。默认是 10 秒。最小值是 1。
- timeoutSeconds：探测的超时时间。默认值是 1 秒。最小值是 1。
- successThreshold：探测器在失败后，被视为成功的最小连续成功数。默认值是 1。存活探测的这个值必须是 1。最小值是 1。
- failureThreshold：当探测失败时，Kubernetes 的重试次数。存活探测情况下的放弃就意味着重新启动容器。就绪探测情况下的放弃 Pod 会被打上未就绪的标签。默认值是 3。最小值是 1。
HTTP 探测器可以在 httpGet 上配置额外的字段：
- host：连接使用的主机名，默认是 Pod 的 IP。也可以在 HTTP 头中设置 “Host” 来代替。
- scheme ：用于设置连接主机的方式（HTTP 还是 HTTPS）。默认是 HTTP。
- path：访问 HTTP 服务的路径。
- httpHeaders：请求中自定义的 HTTP 头。HTTP 头字段允许重复。
- port：访问容器的端口号或者端口名。如果数字必须在 1 ～ 65535 之间。
相关阅读
2、Kubernetes K8S之Pod 生命周期与init container初始化容器
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