Health Check Endpoint in Node.js: Liveness vs Readiness

Your load balancer is routing traffic to a server whose database connection pool is exhausted. Docker restarted a container that never finished its startup migrations. Kubernetes replaced a healthy pod because the liveness probe hit an endpoint that returned 503 on a transient Redis timeout. All of these happen because /health returned the wrong thing — or because nobody designed it carefully enough. A health check endpoint is not a ping. It is the interface between your application and the in