Redis-exporter multi-target:
Redis-exporter multi-target: /metrics endpoint ignores ?target= query param — must use /scrape endpoint. Pre-existing silent bug: Prometheus redis job used default metrics_path: /metrics with multi-target redis-exporter relabeling. The /metrics endpoint only scrapes localhost:6379 (which does not exist so redis_up 0). All 18 Redis instances appeared permanently down. Fix: add metrics_path: /scrape to redis job in /opt/prometheus/prometheus.yml. Verification: curl http://redis-exporter:9121/scrape?target=redis://name:6379 | grep redis_up must return 1.