Pod Lifecycle Hooks

Lifecycle hooks allow containers to be aware of events in their management lifecycle and run code when they occur.

Types of Hooks

1. postStart

Executed immediately after a container is created. Does NOT wait for the container process to start.

2. preStop

Executed just before a container is terminated. Gives containers time to gracefully shut down.

Hook Handler Types

Exec

Executes a specific command inside the container.

postStart:
  exec:
    command: ["/bin/sh", "-c", "echo 'Container started'"]

HTTPGet

Makes an HTTP request to a specified endpoint.

postStart:
  httpGet:
    host: localhost
    port: 8080
    path: /init

TCPSocket

Performs a TCP check against a specific port.

preStop:
  tcpSocket:
    port: 5432

Important Notes

• postStart is not guaranteed to execute before ENTRYPOINT - use init containers for setup
• preStop is synchronous - Pod termination waits for preStop to complete
• Failure in preStop hook will cause Pod to immediately terminate
• preStop is useful for cleanup: closing database connections, draining requests, etc.
• postStart failures will restart the container (if RestartPolicy allows)

Example: Graceful Shutdown with preStop

lifecycle:
  preStop:
    exec:
      command: ["/bin/sh", "-c", "sleep 15"]

This gives the application 15 seconds to finish ongoing requests before termination.