Simple multiprocess dockerfile

bash

$ docker build . -t multiprocess-image  # must use --init to get proper signal propagation to background process
$ docker run --init --name multiprocess-container --detach multiprocess-image
$ docker kill -s SIGINT multiprocess-container  # signal will be sent to both processes

Dockerfile

# Sometimes, you want to run a simple background process, as well as your main process, e.g. webserver.
# You can run multiple instances of your container, or you can use s6 or other supervisor tool
#
# Or, you can use a couple of simple tools
FROM ubuntu:22.04
RUN apt update && apt install run-one  # for run-one-constantly
# set up your app here
# tell tini to kill the whole process group, not just the one process
ENV TINI_KILL_PROCESS_GROUP=1
COPY entrypoint.sh /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

entrypoint.sh

#!/bin/bash
set -eu
# restart worker-process if it exists, with backoff
run-one-constantly worker-process &

exec main-process