Docker uses Supervisor to manage process operations

A Docker container starts a single process when it starts, for example, an ssh or apache daemon service.

But we often need to start multiple services on a machine. There are many ways to do this. The simplest way is to put multiple startup commands into a startup script and start the script directly at startup. Another way is to install a process management tool.

This section will use the process management tool supervisor to manage multiple processes in the container. Using Supervisor can better control, manage, and restart the processes we want to run. Here we demonstrate how to use ssh and apache services at the same time.

Configuration

First create a Dockerfile. The contents and parts are explained below.

FROM ubuntu:13.04
MAINTAINER [email protected]
RUN echo "deb http://archive.ubuntu.com/ubuntu precise main universe" > /etc/apt/sources.list
RUN apt-get update
RUN apt-get upgrade -y

Install ssh, apache and supervisor

RUN apt-get install -y openssh-server apache2 supervisor
RUN mkdir -p /var/run/sshd
RUN mkdir -p /var/log/supervisor

Here, 3 software are installed, and 2 directories required for the normal operation of ssh and supervisor services are created.

COPY supervisord.conf /etc/supervisor/conf.d/supervisord.conf

Add the supervisord configuration file and copy it to the corresponding directory.

EXPOSE 22 80

CMD ["/usr/bin/supervisord"]

Here we map ports 22 and 80 and start the service using the executable path of supervisord.

Supervisor configuration file content

[supervisord]
nodaemon=true
[program:sshd]
command=/usr/sbin/sshd -D
[program:apache2]
command=/bin/bash -c "source /etc/apache2/envvars && exec /usr/sbin/apache2 -DFOREGROUND"

The configuration file contains directories and processes. The first section, supervsord, configures the software itself and runs it with the nodaemon parameter. The second section contains the 2 services to be controlled. Each section contains a service directory and the command to start the service.

How to use

Create an image.

$ sudo docker build -t test/supervisord .

Start the supervisor container.

$ sudo docker run -p 22 -p 80 -t -i test/supervisords
2013-11-25 18:53:22,312 CRIT Supervisor running as root (no user in config file)
2013-11-25 18:53:22,312 WARN Included extra file "/etc/supervisor/conf.d/supervisord.conf" during parsing
2013-11-25 18:53:22,342 INFO supervisord started with pid 1
2013-11-25 18:53:23,346 INFO spawned: 'sshd' with pid 6
2013-11-25 18:53:23,349 INFO spawned: 'apache2' with pid 7

Use docker run to start the container we created. Use multiple -p to map multiple ports so that we can access ssh and apache services at the same time.

You can use this method to create a base image with only the ssh service, and then create images based on this image.

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