simple-docker-host

WARNING: Experimental.

Configure a minimilist Ubuntu 12.04 LTS host running Docker, Upstart and an nginx forwarding proxy. Deploy arbitrary services packaged as Docker containers.

Services are represented as git repositories containing a Dockerfile, an upstart.conf, and an optional nginx-proxy.conf. Services can be created and deployed with a single git push thanks to gitreceive.

How is this different from Dokku/Flynn/Deis/CoreOS/etc?

Right now, there are a bunch of interesting projects trying to make it easy to deploy services with Docker:

• Dokku provides a miniature Heroku-like environment. It's tiny and clever, but less useful if you want to deploy non-web services.
• Flynn is intended to be a much more ambitous version of Dokku, but it's still under development.
• Deis uses Chef to manage services like databases, and a Heroku-style interface to manage web apps. It will soon be able to deploy web apps described using a Dockerfile, but that's not released yet.
• CoreOS is very clever: It's a bare Linux system running systemd (to manage servers) and etcd (to control cluster configuration). Unfortunately, it's hard to get running on many web hosts, and it's still early in its development cycle. And as far as I know, it doesn't offer any git push-based deployment mechanisms.
• It's also possible to deploy Docker on top of OpenStack, assuming you have an OpenStack environment.

But none of these quite meet my needs yet. I'm looking for a system which:

• Is small enough to be installed on a "hobby" server.
• Allows arbitrary docker services to be deployed using git push, including web apps, mail servers, or anything else which can be containerized.
• Provides a forwarding proxy server which can route requests to the correct web app.
• Can be deployed in minutes to almost any hosted Ubuntu 12.04 LTS server running Linux 3.8 or later.
• Can be run locally with Vagrant for development and testing.
• Is small and unobtrusive enough to be thrown away once one of the above projects matures.

The solution: a low-rent CoreOS knockoff using git push to create and deploy images, and Upstart to manage running containers.

Running locally with Vagrant

To build and provision a server in Vagrant:

vagrant up

To configure your account on the server:

cat ~/.ssh/id_rsa.pub | vagrant ssh -c "sudo gitreceive upload-key `whoami`"

To deploy a project to the server, make sure it has a Dockerfile and an upstart.conf file telling Upstart how to run it (see below). Then run:

git remote add docker-dev git@docker-dev.local:myproject.git
git push docker-dev master

This should create the remote git repository, build a docker image named myproject, install myproject.conf, and restart the server.

Running on a hosted Ubuntu server

Make sure the remote server is running Ubuntu 12.04 LTS with Linux kernel 3.8 or greater. See the official Ubuntu instructions for details on updating the kernel, but don't bother installing docker itself yet. For Linode, see their blog. For other hosting environments, search the web.

Take a momement to disable any unnecessary services, turn on automatic updates, and do any other standard server configuration you like to do. The goal is produce a server with nothing much except an ssh daemon and (typically) ntp and dhcp.

Once your server is ready, upload and run the configure-system.sh script as root. This should finish configuring the system. This script is "idempotent", in the usual DevOps sense, which means if you run it more than once, it shouldn't cause any problems.

Finally, make sure that you can log into the remote server via ssh and use sudo. To do, this you will probably need to run visudo and edit /etc/sudoers as follows:

%sudo   ALL=(ALL:ALL) NOPASSWD: ALL

Then add your regular account to the sudo group:

usermod -a -G sudo myaccount

Once that's in place, run:

cat ~/.ssh/id_rsa.pub | ssh example.com sudo gitreceive upload-key `whoami`
git remote add myserver git@example.com:myproject.git

Note that this makes your regular account and the git account both equivalent to the root account. You can remove your own account from the sudo group once your key is set up. But the git account needs to retain full privileges, because it needs to be able to deploy arbitrary services. That's the whole point of this exercise.

An example service

Create a repository containing the following Dockerfile:

FROM ubuntu:12.04

ENV DEBIAN_FRONTEND noninteractive
ENV APACHE_LOG_DIR /var/log/apache2
ENV APACHE_RUN_USER www-data
ENV APACHE_RUN_GROUP www-data

RUN apt-get update
RUN apt-get install -y apache2

EXPOSE 80

CMD /usr/sbin/apache2 -DFOREGROUND

...and the following upstart.conf file:

description "Apache 2 demo server"
author "Eric Kidd"
start on filesystem and started docker
stop on runlevel [!2345]
respawn
console log
kill signal SIGINT
exec /usr/bin/docker run -rm -p 127.0.0.1:8000:80 apache2-demo

Here, we bind port 80 on the container to port 8000 on the host's internal interface. If we were setting up a public mail server, we would use -p 25:25 to bind port 25 on the container to port 25 on the host. But in the case of port 80, we're going to want to share it between multiple containers using a forwarding proxy. To do this, we need to add a third file, nginx-proxy.conf:

server {
  listen 80 default_server;

  # Run as a catch-all server for demo purposes.
  server_name _;

  # Alternatively, see http://wiki.nginx.org/ServerBlockExample for examples
  # on how to set up multiple sites with different hostnames.
  #server_name vhost.example.com;

  location / {
    proxy_pass http://127.0.0.1:8000/;
  }
}

Commit these three files using git and run:

git init
git add Dockerfile upstart.conf nginx-proxy.conf
git commit -m "Create sample apache project"
git remote add docker-dev git@docker-dev.local:apache2-demo.git
git push docker-dev master

Once this is up and running, visit the following URL in your browser:

http://docker-dev.local/