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Kubernetes三种探针

发表者:admin分类:云计算容器2022-01-06 23:29:30 阅读[570]


Kubernetes三种探针


k8s支持存活livenessProbe和就绪readinessProbe两种探针,两种探针都支持以下三种方式

一、exec

通过执行shell命令的方式,判断退出状态码是否是0,示例:

      exec:
        command:
        - cat
        - /tmp/healthy

二、tcp

通过TCP请求的方式,是否能建立tcp连接,示例:

      tcpSocket:
        port: 8080
      initialDelaySeconds: 15
      periodSeconds: 20

三、httpGet

通过发起http请求,判断返回结果是否符合预期,示例:

...
livenessProbe:
     httpGet:
       path: /healthz
       port: 8080
       httpHeaders:
       - name: X-Custom-Header
         value: Awesome
       initialDelaySeconds: 3
       periodSeconds: 3

  • initialDelaySeconds指定了容器启动后多少秒后进行探测

  • periodSeconds指定每隔多少秒进行探测

 

Liveness 探测


Liveness 探测让用户可以自定义判断容器是否健康的条件。如果探测失败,Kubernetes 就会重启容器。还是举例说明,创建如下 Pod:
启动进程首先创建文件 /tmp/healthy,30 秒后删除,在我们的设定中,如果 /tmp/healthy 文件存在,则认为容器处于正常状态,反正则发生故障。

[root@k8s-master ~]# cat liveness.yml 
apiVersion: v1
kind: Pod
metadata:
  name: liveness-pod
  namespace: default
spec:
    restartPolicy: OnFailure
    containers:
    - name: myapp
      image: busybox
      imagePullPolicy: IfNotPresent
      command: ["/bin/sh","-c","touch /tmp/healthy;sleep 30;rm -rf /tmp/healthy;sleep 3600"]
      livenessProbe:
        exec:
          command: ["test","-e","/tmp/healthy"]
        initialDelaySeconds: 5
        periodSeconds: 5

livenessProbe 部分定义如何执行 Liveness 探测:

  1. 探测的方法是:通过 test命令检查 /tmp/healthy 文件是否存在。如果命令执行成功,返回值为零,Kubernetes 则认为本次 Liveness 探测成功;
    如果命令返回值非零,本次 Liveness 探测失败。

  2. initialDelaySeconds:5 指定容器启动 5s之后开始执行 Liveness 探测,我们一般会根据应用启动的准备时间来设置。
    比如某个应用正常启动要花 30 秒,那么 initialDelaySeconds 的值就应该大于 30。

  3. periodSeconds: 5 指定每 5 秒执行一次 Liveness 探测。Kubernetes 如果连续执行 3 次 Liveness 探测均失败,则会杀掉并重启容器。

 下面创建 Pod liveness

[root@k8s-master ~]# kubectl apply -f liveness.yml 
pod/liveness-pod created

 从配置文件可知,最开始的 30 秒,/tmp/healthy 存在,test 命令返回 0,Liveness 探测成功,这段时间 kubectl describe pod liveness 的 Events部分会显示正常的日志。

[root@k8s-master ~]# kubectl describe pod  liveness-pod 
Events:
  Type    Reason     Age        From                 Message
  ----    ------     ----       ----                 -------
  Normal  Scheduled  <unknown>  default-scheduler    Successfully assigned default/liveness-pod to k8s-master
  Normal  Pulled     12s        kubelet, k8s-master  Container image "busybox" already present on machine
  Normal  Created    11s        kubelet, k8s-master  Created container myapp
  Normal  Started    11s        kubelet, k8s-master  Started container myapp

35 秒之后,日志会显示 /tmp/healthy 已经不存在,Liveness 探测失败。再过几十秒,几次探测都失败后,容器会被重启。

[root@k8s-master ~]# kubectl describe pod   liveness-pod 
Command:
      /bin/sh
      -c
      touch /tmp/healthy;sleep 30;rm -rf /tmp/healthy;sleep 3600
    State:          Running
      Started:      Fri, 06 Nov 2020 15:40:59 +0800
    Last State:     Terminated
      Reason:       Error
      Exit Code:    137   #可以看到退出了,OnFailure : 容器终止运行且退出码不为0时重启
      Started:      Fri, 06 Nov 2020 15:39:45 +0800
      Finished:     Fri, 06 Nov 2020 15:40:59 +0800
    Ready:          True
    Restart Count:  1    #容器重启了1次
    Liveness:       exec [test -e /tmp/healthy] delay=5s timeout=1s period=5s #success=1 #failure=3
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-dfmvc (ro)
Events:
  Type     Reason     Age                 From                 Message
  ----     ------     ----                ----                 -------
  Normal   Scheduled  <unknown>           default-scheduler    Successfully assigned default/liveness-pod to k8s-master
  Warning  Unhealthy  55s (x3 over 65s)   kubelet, k8s-master  Liveness probe failed:
  Normal   Killing    55s                 kubelet, k8s-master  Container myapp failed liveness probe, will be restarted  #可以看到健康检查失败
  Normal   Pulled     25s (x2 over 100s)  kubelet, k8s-master  Container image "busybox" already present on machine
  Normal   Created    25s (x2 over 99s)   kubelet, k8s-master  Created container myapp
  Normal   Started    25s (x2 over 99s)   kubelet, k8s-master  Started container myapp


[root@k8s-master ~]# kubectl get pod -o wide
NAME           READY   STATUS    RESTARTS   AGE     IP            NODE         NOMINATED NODE   READINESS GATES
liveness-pod   1/1     Running   3          4m20s   10.244.0.27   k8s-master   <none>           <none>

 除了 Liveness 探测,Kubernetes Health Check 机制还包括 Readiness 探测,下篇博客见。



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