Kubernetes Health Probes

Mechanism for the kubelet to check the health and readiness of containers.

Edit Concept ✏️

Kubernetes Health Probes

Probes allow Kubernetes to monitor the health of your applications and take automatic action when things go wrong.

1. Liveness Probe

  • Goal: Is the container alive?
  • Action: If it fails, the kubelet kills the container and restarts it (based on the restart policy).
  • Use Case: Catching deadlocks where the app is running but can’t do anything.

2. Readiness Probe

  • Goal: Is the container ready to serve traffic?
  • Action: If it fails, the container’s IP is removed from all Services (endpoints). Traffic is stopped until it passes again.
  • Use Case: During app startup (loading big files, connecting to DB) or when an app is temporarily overloaded.

3. Startup Probe

  • Goal: Has the application started?
  • Action: All other probes are disabled until the startup probe succeeds.
  • Use Case: Legacy apps that take a long time to boot. It prevents the Liveness probe from killing the container before it finishes starting up.

Probe Mechanisms

  • HTTP GET: Returns a 2xx or 3xx status code.
  • TCP Socket: Can a TCP connection be established on a specific port?
  • Exec: Run a command inside the container. Exit code 0 is success.
  • gRPC: Uses the gRPC Health Checking Protocol.