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 ifthe
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 forthe 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 (inseconds) to perform the probe. Default to 10 seconds. Minimum
value is 1.
successThreshold <integer>
Minimum consecutive successes forthe probe to be considered successful
after having failed. Defaults to 1. Must be 1 forliveness. 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 whichthe probe timesout. 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
