semaphore-exporter

Prometheus exporter for Semaphore, which has no native /metrics endpoint. Polls Semaphore's REST API (cached briefly so a scrape storm can't hammer it) and serves Prometheus text format. Read-only — only ever GETs, never starts/stops/modifies a task or template. Stdlib-only Python, no third-party dependencies.

Notably exports semaphore_task_running_seconds for every non-terminal task, so a task stuck running for hours (not just failed/succeeded ones) shows up — see the module docstring in exporter.py for the incident that motivated it.

Build

docker build -t semaphore-exporter:latest .

Run

docker run -d --name semaphore-exporter --restart unless-stopped \
  -p 9825:9825 \
  -e SEMAPHORE_URL=http://semaphore:3000 \
  -e SEMAPHORE_API_TOKEN=<token> \
  semaphore-exporter:latest

Scrape :9825/metrics with Prometheus.