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Kubernetes Healthcheck

对 Pod 的健康状态检查可以通过两类探针来检查：LivenessProbe 和 ReadinessProbe。

LivenessProbe ：用于判断容器是否存活，如果 LivenessProbe 探针探测到容器不健康，则 kubelet 将杀掉容器，并根据容器的启动策略做相应的处理，如果一个容器不包括 LivenessProbe 探针，kubelet 认为该容器的 LivenessProbe 探针返回的值永远是 Success。
ReadinessProbe：用于判断容器是否启动完成（ready 状态），可以接受请求，如果 ReadinessProbe 探针检测到失败，则 Pod 的状态则被更改。

1）ExecAction ：容器内不执行一个命令，如果该命令的返回码为 0 ，则表示容器健康,15秒探测一次，超时1秒后会重启服务。

kind: ...
spec:
  containers:
  - name: ..
    livenessProbe:
     exec:
     command:
      - cat
      - /tmp/health
      initialDelaySeconds: 15
      timeoutSeconds: 1

2）TCPSocketAction：通过容器的 IP 地址和端口号执行 TCP 检查，如果能够建立 TCP 连接，则表明容器健康。

...
spec:
  containers:
  - name: 
  ...
    livenessProbe:
      tcpSocket:
        port: 80
      initialDelaySeconds: 30
      timeoutSeconds: 1

3）HTTPGETAction：通过容器的 IP 地址，端口及路径调用 HTTP GET 方法，如果响应的状态码大于等于 200 且小于 400，则任务健康,访问的路径是 localhost:80/_status/healthz

...
spec:
  containers:
  - ports:
  ...
    livenessProbe:
      httpGet:
        path: /_status/healthz
        port: 80
      initialDelaySeconds: 30
      timeoutSeconds: 1

它们的含义分别如下：

initialDelaySeconds：启动容器后进行首次健康检查的等待时间，单位为 s 。
timeutSeconds：健康检查发送请求后等待相应的超时时间，单位为 s。当超时发生时，kubeler 会认为容器已经无法提供服务，将会重启该容器。
initialDelaySeconds：检查开始执行的时间，以容器启动完成为起点计算
periodSeconds：检查执行的周期，默认为10秒，最小为1秒
timeoutSeconds：检查超时的时间，默认为1秒，最小为1秒
successThreshold：从上次检查失败后重新认定检查成功的检查次数阈值（必须是连续成功），默认为1
failureThreshold：从上次检查成功后认定检查失败的检查次数阈值（必须是连续失败），默认为1
httpGet的属性
- host：主机名或IP
- scheme：链接类型，HTTP或HTTPS，默认为HTTP
- path：请求路径
- httpHeaders：自定义请求头
- port：请求端口

定义说明如下：

$ kubectl explain pod.spec.containers.livenessProbe
KIND:     Pod
VERSION:  v1

RESOURCE: livenessProbe <Object>

DESCRIPTION:
     Periodic probe of container liveness. Container will be restarted if the
     probe fails. Cannot be updated. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes

     Probe describes a health check to be performed against a container to
     determine whether it is alive or ready to receive traffic.

FIELDS:
   exec	<Object>
     One and only one of the following should be specified. Exec specifies the
     action to take.

   failureThreshold	<integer>
     Minimum consecutive failures for the probe to be considered failed after
     having succeeded. Defaults to 3. Minimum value is 1.

   httpGet	<Object>
     HTTPGet specifies the http request to perform.

   initialDelaySeconds	<integer>
     Number of seconds after the container has started before liveness probes
     are initiated. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes

   periodSeconds	<integer>
     How often (in seconds) to perform the probe. Default to 10 seconds. Minimum
     value is 1.

   successThreshold	<integer>
     Minimum consecutive successes for the probe to be considered successful
     after having failed. Defaults to 1. Must be 1 for liveness. Minimum value
     is 1.

   tcpSocket	<Object>
     TCPSocket specifies an action involving a TCP port. TCP hooks not yet
     supported

   timeoutSeconds	<integer>
     Number of seconds after which the probe times out. Defaults to 1 second.
     Minimum value is 1. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes

startupProbe

新增 startupProbe, 主要解决 livenessProbe 启动时，如果无法正常启动或服务启动时间较长引起的容器重新启动的问题。

apiVersion: apps/v1
kind: Deployment
metadata:
  name: busybox-lifecycles-nginx-sleep
spec:
  replicas: 2
  selector:
    matchLabels:
      app: busybox-lifecycles-nginx-sleep
      env-o: nginx-sleep
  template:
    metadata:
      labels:
        app: busybox-lifecycles-nginx-sleep
        env-o: nginx-sleep
      annotations:
        consul.hashicorp.com/connect-inject: "true"
    spec:
      terminationGracePeriodSeconds: 120
      containers:
      - image: slzcc/terminal-ctl:ubuntu-20.04
        imagePullPolicy: Always
        command:
          - nginx
          - -g
          - daemon off;
        name: busybox
        livenessProbe:
          exec:
            command:
            - /bin/bash
            - -c
            - nc -z -v -n 127.0.0.1 80
          failureThreshold: 10
          initialDelaySeconds: 5
          periodSeconds: 10
          successThreshold: 1
          timeoutSeconds: 5
        readinessProbe:
          exec:
            command:
            - /bin/bash
            - -c
            - nc -z -v -n 127.0.0.1 80
          initialDelaySeconds: 5
          periodSeconds: 10
        startupProbe:
          httpGet:
            path: /
            port: 801
          failureThreshold: 3
          periodSeconds: 10
      restartPolicy: Always

---
apiVersion: v1
kind: Service
metadata:
  name: busybox-lifecycles-nginx-sleep
  labels:
    app: busybox-lifecycles-nginx-sleep
spec:
  ports:
   - name: http
     port: 80
     targetPort: 80
     protocol: TCP
  selector:
    app: busybox-lifecycles-nginx-sleep

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startupProbe