Architecting for Observability: Implementing Health Checks and Liveness/Readiness Probes

Differentiate between Liveness (is the process alive?) and Readiness (is the process ready to serve traffic?) to ensure orchestration tools like Kubernetes don't route traffic to a failing or warming-up instance.

In a robust Node.js architecture, a simple 200 OK heartbeat is insufficient. A Liveness probe should detect if the process is in a deadlock or infinite loop (V8/Event Loop freeze). A Readiness probe should verify that downstream dependencies (DB, Redis, RabbitMQ) are reachable and that the app has finished initial startup tasks. If a readiness probe fails, the load balancer removes the instance from the rotation but doesn't kill it. If the liveness probe fails, the orchestrator restarts the container.