Kubernetes Container Lifecycle Events

Lifecycle Hook

İki tane lifecycle hook var. Açıklaması şöyle

PostStart: This hook is executed right after a container is created. However, the hook might be invoked after the container's ENTRYPOINT is executed. The hook handler must not accept any parameters.

PreStop: This hook is executed immediately before a container is terminated due to any reason, such as resource contention, liveness probe failure, etc. You cannot pass any parameters to the handler, and the container will be terminated irrespective of the outcome of the handler.

Lifecycle Hook Handlers

Hook'a iki çeşit handler takabiliriz. Açıklaması şöyle

There are two types of handlers that you can attach to a lifecycle hook:

exec: It executes the specified command in the container's main process. The command is executed in parallel with the container's ENTRYPOINT instruction. If the hook takes too long or fails, the kubelet process will restart the container.

httpGet or tcpSocket: It sends an HTTP request or establishes a TCP socket connection against a specific endpoint on the container. Unlike the exec, which is executed by the container, this handler is executed by the kubelet process.

Örnek - postStart

Şöyle yaparız

apiVersion: v1
kind: Pod
metadata:
  name: sidecar-container-demo
spec:
  containers:
    - image: busybox
      command: ["/bin/sh"]
      args:
        [
          "-c",
          "while true; do echo echo $(date -u) 'Written by busybox sidecar container' >> /var/log/index.html; sleep 5;done",
        ]
      name: sidecar-container
      resources: {}
      volumeMounts:
        - name: var-logs
          mountPath: /var/log
      lifecycle:
        postStart:
          httpGet:
            path: /index.html
            port: 80
            host: localhost
            scheme: HTTP
    - image: nginx
      name: main-container
      resources: {}
      ports:
        - containerPort: 80
      volumeMounts:
        - name: var-logs
          mountPath: /usr/share/nginx/html
  dnsPolicy: Default
  volumes:
    - name: var-logs
      emptyDir: {}

Örnek - preStop

Şöyle yaparız

apiVersion: v1
kind: Pod
metadata:
  name: prestop-demo
spec:
  containers:
    - image: nginx
      name: nginx-container
      resources: {}
      ports:
        - containerPort: 80
      lifecycle:
        preStop:
          exec:
            command:
              - sh
              - -c
              - echo "Stopping container now...">/proc/1/fd/1 && nginx -s stop
  dnsPolicy: Default