How to start a daemon in background during Docker container startup?

I am trying to run a custom Python-based server (queue server) daemon in a Docker container, which communicates via sockets and operates similarly to standard Linux daemons.

The server works when started manually inside the container:

docker exec -it my_container /bin/bash
/usr/queue/qserver --port=1234 &

However, I want the daemon to run, right after calling docker run. I've tried these approaches in my Dockerfile:

Using CMD with background process:

CMD /usr/queue/qserver --port=1234 & sleep infinity

Using an entrypoint script:

#!/bin/bash
/usr/queue/qserver --port=1234 &
sleep infinity

But when check the qserver daemon is not running.

How can I ensure the qserver starts and remains running when the container launches?

Solution

Docker containers differ fundamentally from traditional Linux systems in process management. While Linux systems have a complete init system (PID 1) managing all processes, Docker containers run with a single main process that must handle all process management duties.

Direct Background Process:

CMD ["./daemon", "&"]

Init System:

CMD ["tini", "--", "./daemon"]

Process Supervisor:

CMD ["supervisor", "./daemon"]

Choose appropriate process management strategy
Implement proper signal handling (SIGTERM, SIGINT)
Enable logging and monitoring
Handle startup dependencies Design for proper container shutdown

in short:

Simple daemons → lightweight init system

Complex daemons → process supervisor

Critical services → full monitoring and health checks