How to start multiple processes in Docker?

About

To run multiple services in a single container there are multiple ways

• with a basic script
• via a process manager

Solutions

Script

With a script:

• you start any number of programs in the background,
• and you start a process at the end that stay in the foreground to keep the VM alive.

Example of script:

• background process (&)
• and the fg (foreground utility)

#!/bin/bash
set -m # to make job control work
/app/server &
/app/server -bar &
fg %1 

Docker file with the ENTRYPOINT instruction

ADD multiple.sh /app/
ENTRYPOINT /app/multiple.sh

Process Manager

A process manager can start more than one process.

Example with overmind

• A Procfile with two commands:

web: bundle exec rails server -p $PORT
foo: /app/foo

• Docker and the overmind procfile manager

ADD Procfile /app/
CMD overmind start