Docker multiple entrypoints

Question

Say I have the following Dockerfile:

FROM ubuntu

RUN apt-get update
RUN apt-get install -y apache2
RUN apt-get install -y mongod #pretend this exists

EXPOSE 80

ENTRYPOINT ["/usr/sbin/apache2"]

The ENTRYPOINT command makes it so that apache2 starts when the container starts. I want to also be able to start mongod when the the container starts with the command service mongod start. According to the documentation however, there must be only one ENTRYPOINT in a Dockerfile. What would be the correct way to do this then?

Answer 1

As Jared Markell said, if you wan to launch several processes in a docker container, you have to use supervisor. You will have to configure supervisor to tell him to launch your different processes.

I wrote about this in this blog post, but you have a really nice article here detailing how and why using supervisor in Docker.

Basically, you will want to do something like:

FROM ubuntu

RUN apt-get update
RUN apt-get install -y apache2
RUN apt-get install -y mongod #pretend this exists
RUN apt-get install -y supervisor # Installing supervisord

ADD supervisord.conf /etc/supervisor/conf.d/supervisord.conf 

EXPOSE 80

ENTRYPOINT ["/usr/bin/supervisord"]

And add a configuration a file supervisord.conf

[supervisord]
nodaemon=true

[program:mongodb]
command=/etc/mongod/mongo #To adapt, I don't know how to launch your mongodb process

[program:apache2]
command=/usr/sbin/apache2 -DFOREGROUND

---

EDIT: As this answer has received quite lot of upvotes, I want to precise as a warning that using Supervisor is not considered as a best practice to run several jobs. Instead, you may be interested in creating several containers for your different processes and managing them through docker compose. In a nutshell, Docker Compose allows you to define in one file all the containers needed for your app and launch them in one single command.

Answer 2

My solution is to throw individual scripts into /opt/run/ and execute them with:

#!/bin/bash

LOG=/var/log/all

touch $LOG

for a in /opt/run/*
do
    $a >> $LOG &
done

tail -f $LOG

And my entry point is just the location of this script, say it's called /opt/bin/run_all:

ADD 00_sshd /opt/run/
ADD 01_nginx /opt/run/

ADD run_all /opt/bin/
ENTRYPOINT ["/opt/bin/run_all"]

Answer 3

The simple answer is that you should not because it breaks the single responsibility principle: one container, one service. Imagine that you want to spawn additional cloud images of MongoDB because of a sudden workload - why increasing Apache2 instances as well and at a 1:1 ratio? Instead, you should link the boxes and make them speak through TCP. See https://docs.docker.com/userguide/dockerlinks/ for more info.