Server alerts started firing: disk at 95%. We SSH'd in expecting log files. Instead: 180GB of Docker data. Old images, stopped containers, orphaned volumes—months of build artifacts nobody cleaned up.

How It Happened

Every CI/CD deploy pulled a new image. Old ones stayed. Every failed container left layers behind. Docker's default behavior keeps everything unless you tell it not to.

The Cleanup

docker system prune -a --volumes

That single command freed 160GB. Then we set up a weekly cron job to prune unused images and added disk usage alerts at 70% instead of 95%.

Prevention

• Automated weekly docker system prune
• Disk alerts at 70% and 85%
• Image retention policy: keep last 5 builds only