Что такое liveness, readiness и startup пробы в Kubernetes?

In Kubernetes, probes are used to check the health of containers and manage their lifecycle. There are three main types of probes:

1. Liveness Probe:

• Checks if the container is alive.
• If the probe fails, Kubernetes restarts the container.
• Used to detect hung or 'dead' processes.

2. Readiness Probe:

• Checks if the container is ready to accept traffic.
• If the probe fails, the container is removed from services and load balancers.
• Prevents sending requests to a container that is not yet initialized.

3. Startup Probe:

• Used to verify the successful start of an application.
• Allows setting a longer timeout for startup, so the container is not considered failed too early.
• After a successful startup probe, Kubernetes switches to using the liveness probe.

Example: If an application takes a long time to start, you can configure a startup probe with a longer timeout to avoid restarting the container prematurely. After startup, liveness and readiness probes monitor the application's state and readiness.