1. The default health check mechanism in K8s
k8s has a powerful self-healing capability, and the default self-healing implementation is to automatically restart the failed container.
So how does k8s discover container failures? Each container will execute a process when it starts, and this process is specified by the CMD or ENTRYPOINT of the Dockerfile. If the return code is non-zero when the process exits, the container is considered to be faulty, and K8s will restart the container according to the restartPolicy policy.
Let's use an example to demonstrate this situation: first write a file to create a pod, the content is as follows:
[root@master pod]# more healthcheck-pod.yml
apiVersion: v1
kind: Pod
metadata:
name: pod-healthcheck
labels:
test: healthcheck-test
spec:
restartPolicy: OnFailure
containers:
- name: healthcheck
image: busybox
args:
- /bin/sh
- -c
- sleep 10; exit 1 #sleep 10; exit 1 模拟容器启动 10 秒后发生故障
Next, execute the pod to check the status of the pod:
[root@master pod]# kubectl apply -f healthcheck-pod.yml
[root@master pod]# kubectl get pod
NAME READY STATUS RESTARTS AGE
pod-healthcheck 0/1 CrashLoopBackOff 5 8m<