Debug: Docker container exits immediately

Docker container starts and immediately exits with code 0 or 1. docker ps shows nothing running.

Diagnosis steps:

1. Check exit code and logs:

docker ps -a # shows stopped containers
docker logs <container_id>

1. Common causes:

- No foreground process: CMD runs a background daemon. Fix: run in foreground mode
- Script exits: entrypoint script completes without keeping process alive
- Missing dependency: app crashes on startup

1. Debug interactively:

docker run -it --entrypoint /bin/sh <image>

1. Keep container alive for debugging:

docker run -d <image> tail -f /dev/null
docker exec -it <container_id> /bin/sh

1. For exit code 137: OOM killed. Increase memory limit:

docker run --memory=512m <image>

Docker requires a foreground process to keep running. When the main process (PID 1) exits, the container stops.