Prometheus Targets DOWN: Scrape Debug in 4 Steps

Symptom

Target list shows targets in DOWN state; no metrics arriving.

Root cause

Exporter dead, DNS/service discovery stale, or scrape path/port wrong.

Fix, in order

1. Read the actual scrape error on the target pagehttp://prom:9090/targets # "server returned HTTP 404" etc.
2. Hit the metrics path yourselfcurl -v http://exporter:9100/metrics
3. Verify service discovery labels match reality# kubernetes_sd: check namespace/selector labels

Prevent it coming back

Alert on up == 0 for longer than 5m; blackbox-exporter for user journeys.

Run it on clean infra

Spinning up a fresh box to reproduce or escape this error?

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Last reviewed 2026-10-02 · NinjaOps SEO grid · DevOps blog