Process running but load balancer says unhealthy

WHAT IT TESTS: whether you can separate process liveness from health-check semantics and debug layer by layer. ANSWER OUTLINE: the health probe checks a specific path, port, protocol, and expected status code, any of which can mismatch a running app; a security group or NSG may block the probe source; the app process may be up but not serving the probe endpoint or returning a non-2xx code; timeouts and thresholds may be too strict. Troubleshoot by curling the exact probe URL from the LB's perspective and reading probe logs.