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page_title: Using Supervisor with Docker page_description: How to use Supervisor process management with Docker page_keywords: docker, supervisor, process management
Using Supervisor with Docker
Note:
- If you don't like sudo then see Giving non-root access
Traditionally a Docker container runs a single process when it is
launched, for example an Apache daemon or a SSH server daemon. Often
though you want to run more than one process in a container. There are a
number of ways you can achieve this ranging from using a simple Bash
script as the value of your container's CMD
instruction to installing
a process management tool.
In this example we're going to make use of the process management tool, Supervisor, to manage multiple processes in our container. Using Supervisor allows us to better control, manage, and restart the processes we want to run. To demonstrate this we're going to install and manage both an SSH daemon and an Apache daemon.
Creating a Dockerfile
Let's start by creating a basic Dockerfile
for our
new image.
FROM ubuntu:13.04
MAINTAINER examples@docker.io
RUN echo "deb http://archive.ubuntu.com/ubuntu precise main universe" > /etc/apt/sources.list
RUN apt-get update
RUN apt-get upgrade -y
Installing Supervisor
We can now install our SSH and Apache daemons as well as Supervisor in our container.
RUN apt-get install -y openssh-server apache2 supervisor
RUN mkdir -p /var/run/sshd
RUN mkdir -p /var/log/supervisor
Here we're installing the openssh-server
,
apache2
and supervisor
(which provides the Supervisor daemon) packages. We're also creating two
new directories that are needed to run our SSH daemon and Supervisor.
Adding Supervisor's configuration file
Now let's add a configuration file for Supervisor. The default file is
called supervisord.conf
and is located in
/etc/supervisor/conf.d/
.
ADD supervisord.conf /etc/supervisor/conf.d/supervisord.conf
Let's see what is inside our supervisord.conf
file.
[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 supervisord.conf
configuration file contains
directives that configure Supervisor and the processes it manages. The
first block [supervisord]
provides configuration
for Supervisor itself. We're using one directive, nodaemon
which tells Supervisor to run interactively rather than
daemonize.
The next two blocks manage the services we wish to control. Each block
controls a separate process. The blocks contain a single directive,
command
, which specifies what command to run to
start each process.
Exposing ports and running Supervisor
Now let's finish our Dockerfile
by exposing some
required ports and specifying the CMD
instruction
to start Supervisor when our container launches.
EXPOSE 22 80
CMD ["/usr/bin/supervisord"]
Here We've exposed ports 22 and 80 on the container and we're running
the /usr/bin/supervisord
binary when the container
launches.
Building our image
We can now build our new image.
$ sudo docker build -t <yourname>/supervisord .
Running our Supervisor container
Once We've got a built image we can launch a container from it.
$ sudo docker run -p 22 -p 80 -t -i <yourname>/supervisord
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
. . .
We've launched a new container interactively using the docker run
command.
That container has run Supervisor and launched the SSH and Apache daemons with
it. We've specified the -p
flag to expose ports 22 and 80. From here we can
now identify the exposed ports and connect to one or both of the SSH and Apache
daemons.