Prometheus scrape target showing as DOWN

Prometheus target shows as DOWN in the targets page. The application is running and the /metrics endpoint works when curled directly.

(1) Check Prometheus can reach the target — network/firewall/namespace issues. (2) Verify the scrape config job matches the target's actual host:port. (3) Check the metrics endpoint path — default is /metrics but some apps use different paths. (4) Verify the response is valid Prometheus format — plain text with TYPE/HELP comments. (5) In Kubernetes, check ServiceMonitor/PodMonitor labels match Prometheus operator's serviceMonitorSelector. (6) Check scrape timeout — if metrics endpoint is slow, increase scrape_timeout.

Prometheus pulls metrics via HTTP GET. Any connectivity issue, wrong path, or invalid response format causes the target to show as DOWN.