Docker storage exhaustion from build cache
A long-running Docker host (used as a self-hosted runner) starts failing container starts with 'no space left on device' on /var/lib/docker, and `df -h` confirms that filesystem is full. The host has been up for months running thousands of CI jobs. `docker system df` shows large 'RECLAIMABLE' figures: dozens of GB in dangling images, stopped containers, anonymous volumes, and build cache. Image churn rose after the team switched to multi-stage builds last month. No application bug. Triage and remediate.
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
0:00 of about 30 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.