Healthcheck

Docker health state and Prometheus’s up series are observations from different checks. A Compose healthcheck runs a command inside the application container. Prometheus independently scrapes a configured metrics endpoint and records whether that scrape succeeded. The two observations can legitimately disagree because an application may refuse useful work while still serving its metrics, or may serve work while its metrics endpoint is broken. ...

A Docker HEALTHCHECK runs a configured command inside a container and records the result as health state. It adds an observation beyond whether the main process is running. The meaning of that observation depends on what the command tests: a process check, an HTTP response, or an application-specific readiness condition. Docker does not infer a universal readiness contract from the presence of the instruction. ...