What are readiness, liveness, and startup probes?

Readiness, liveness, and startup probes are mechanisms for checking the application's state, often used in Kubernetes to manage the lifecycle of containers.

• Readiness probe: Checks if the application is ready to accept traffic. If the probe fails, Kubernetes does not send traffic to this pod.

• Liveness probe: Checks if the application is alive and not hung. If the probe fails, Kubernetes restarts the container.

• Startup probe: Used to verify the successful start of the application. It allows setting a longer timeout for startup to avoid premature container restarts.

Example:

livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 30
  periodSeconds: 10

readinessProbe:
  httpGet:
    path: /ready
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 5

startupProbe:
  httpGet:
    path: /startup
    port: 8080
  failureThreshold: 30
  periodSeconds: 10

Thus, these probes help Kubernetes efficiently manage the application's state and ensure its stable operation.