Docker is another piece of virtualisation-related technology that’s very much ‘in vogue’ at the minute. And for good reason – most of which will be immediately apparent and familiar if you’ve ever worked with FreeBSD’s Jails or Solaris Zones. It’s billed as ‘The Linux container engine’, with a primary goal of providing a framework for self-contained, easily redistributable and deployable images – independantly of hardware, language, operating system, and so on. The upshot really is that it kind of looks and works a lot like the aforementioned Jails or Zones, in that it’s a way of neatly isolating applications or processes within a self-contained environment that doesn’t require a full-blown hypervisor or the typical set of dedicated virtual hardware in order to run. It’s built on top of a few key Linux kernel features, and the Docker project provides the awesomesauce in terms of tooling and framework to make managing and deploying this stuff in a repeatable and easily transferrable manner a snap.
So what can I use it for, you ask? Good question, and one which I hope to explain with an example image that’ll allow you to run your own container hosting another popular bit of open-source software – Owncloud.
First things first and that’s getting Docker installed. I’ll be using Ubuntu 12.04 in my example, so I suggest you follow the existing (and excellent) documentation on getting Docker up and running. Once you’ve managed that we should be on the same page:
# docker version Client version: 0.4.8 Server version: 0.4.8 Go version: go1.1
If you’ve followed the installation document correctly, you’ll have a default set of base images to work with as a starting point for a project such as this. We can see what’s available with the following:
# docker images REPOSITORY TAG ID CREATED SIZE base latest b750fe79269d 3 months ago 24.65 kB (virtual 180.1 MB) base ubuntu-12.10 b750fe79269d 3 months ago 24.65 kB (virtual 180.1 MB) base ubuntu-quantal b750fe79269d 3 months ago 24.65 kB (virtual 180.1 MB) ubuntu 12.10 b750fe79269d 3 months ago 24.65 kB (virtual 180.1 MB) ubuntu latest 8dbd9e392a96 12 weeks ago 131.5 MB (virtual 131.5 MB) ubuntu quantal b750fe79269d 3 months ago 24.65 kB (virtual 180.1 MB)
As we’ll be basing our Owncloud install around LTS, we need to pull in that image specifically:
# docker pull ubuntu:12.04
Once that command completes,
docker images should include the following in its output:
ubuntu 12.04 8dbd9e392a96 3 months ago 131.5 MB (virtual 131.5 MB)
Now we’ve got our starting point it’s on to Owncloud itself.
As you’d probably expect, the base image we’ve pulled in above is relatively sparse and Owncloud has numerous dependancies including Apache httpd and PHP. There’s a few steps we need to run through before we’re able to install the Owncloud package, including grabbing the various dependancies and amending the Apache configuration. While it’s possible to create a new container from the base image and manually run the necessary commands, Docker has a concept known as ‘Dockerfiles’ which allow you to essentially batch all these steps up and have it run through them for you, delivering a built-to-spec image to use. For Owncloud, we’ll need a Dockerfile with the following:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Stick the above into a file called
Dockerfile. This should all look
relatively familiar but there’s a few lines that warrant a bit more
- 6-7, which are needed because Upstart is currently broken in Docker. This is a workaround so that apt’s actions successfully complete;
- 18 tells Docker to NAT port 80 on our host to the container when it’s run;
- 20 is the command that starts Apache’s httpd in the foreground. This is so that Docker can manage the process.
We also need to inject a simple configuration file for Apache into this image
so that it’s included when httpd starts. In the same folder that you’ve saved
this Dockerfile, create a new file called
001-owncloud.conf with the
following basic directives:
<Directory /var/www/owncloud> Options Indexes FollowSymLinks MultiViews AllowOverride All Order allow,deny allow from all </Directory>
Creating an image
Now we’re in a position to go ahead and create our Owncloud image. Run the following command then sit back and watch the magic:
# docker build -t owncloud .
At this point Docker will run through the steps in your Dockerfile and show you the status at each step:
Uploading context 10240 bytes Step 1 : FROM ubuntu:12.04 ---> 8dbd9e392a96 Step 2 : MAINTAINER Nick Jones "firstname.lastname@example.org" ---> Running in bd4ffa2bde51 ---> 5be3042626e5 Step 3 : RUN echo "deb http://archive.ubuntu.com/ubuntu precise main universe" >> /etc/apt/sources.list ---> Running in 6342a8a5bf3a ---> 0a5f6332ccf1 Step 4 : RUN apt-get -y update ---> Running in 5ba451710f4c ---> 25275d3b5080 Step 5 : RUN dpkg-divert --local --rename --add /sbin/initctl ---> Running in 0a0473208260 ---> 927abde6330d Step 6 : RUN ln -s /bin/true /sbin/initctl ---> Running in 92844ba5d028 ---> 21680ab43143 Step 7 : RUN apt-get install -y apache2 php5 php5-gd php-xml-parser php5-intl php5-sqlite smbclient curl libcurl3 php5-curl bzip2 wget vim ---> Running in 0380af0585d2 ---> 2d2684e40291 Step 8 : RUN wget -O - http://download.owncloud.org/community/owncloud-5.0.7.tar.bz2 | tar jx -C /var/www/ ---> Running in f21f8a471b80 ---> dc2c75b30292 Step 9 : RUN chown -R www-data:www-data /var/www/owncloud ---> Running in b9b3e7220075 ---> 74f5580c700b Step 10 : ADD ./001-owncloud.conf /etc/apache2/sites-available/ ---> c0179ce255ef Step 11 : RUN ln -s /etc/apache2/sites-available/001-owncloud.conf /etc/apache2/sites-enabled/ ---> Running in 6ba5513a8432 ---> f96198e6b59d Step 12 : RUN a2enmod rewrite ---> Running in 161a90a9e940 ---> 67cea873cdd7 Step 13 : EXPOSE :80 ---> Running in 9d4cfd17812a ---> 00bd10cd6f7d Step 14 : CMD ["/usr/sbin/apache2ctl", "-D", "FOREGROUND"] ---> Running in 2ccef53a5cfe ---> f0d7dbd897c5 Successfully built f0d7dbd897c5
The output of
docker images should now include our freshly built Owncloud
# docker images | grep owncloud owncloud latest f0d7dbd897c5 About a minute ago 12.29 kB (virtual 779.4 MB)
Running the container
With this built-to-spec image we’re in a position to create a new container which will run our Owncloud ‘stack’, isolated from the host OS and using only the bare essentials:
# docker run -d owncloud d7db4d7c6499
This creates and runs the new container; The
-d switch tells Docker to kick
it off in the background. If successful that command returns a UUID –
d7db4d7c6499 in my case. We can view running containers by doing the
# docker ps ID IMAGE COMMAND CREATED STATUS PORTS d7db4d7c6499 owncloud:latest /usr/sbin/apache2ctl 2 minutes ago Up 2 minutes 80->80
Looks good so far. If you now fire up your browser and point it at your Docker host /owncloud/ you should be greeted by the initial Owncloud setup page asking you to create an Admin user:
Go ahead and do that and you should now be logged into your new Owncloud install, running atop Docker’s various technologies.
So we now have our Owncloud container and our base image, what’s next? Stopping the container is pretty straightforward:
# docker stop d7db4d7c6499 d7db4d7c6499 # docker ps ID IMAGE COMMAND CREATED STATUS PORTS
The output of
docker ps shows us that nothing is currently running. To see all containers, stopped or otherwise, do
docker ps -a:
# docker ps -a ID IMAGE COMMAND CREATED STATUS PORTS d7db4d7c6499 owncloud:latest /usr/sbin/apache2ctl 12 minutes ago Exit 137 2ccef53a5cfe 00bd10cd6f7d /bin/sh -c #(nop) CM 15 minutes ago Exit 0 9d4cfd17812a 67cea873cdd7 /bin/sh -c #(nop) EX 15 minutes ago Exit 0 161a90a9e940 f96198e6b59d /bin/sh -c a2enmod r 15 minutes ago Exit 0 6ba5513a8432 c0179ce255ef /bin/sh -c ln -s /et 15 minutes ago Exit 0 [..]
I’ve snipped the output for brevity, but what’s interesting here to note is
that Docker effectively created a new container from a new image for each step
in our Dockerfile before finally committing that image with the tag we
specified with the
To restart our container, run the following:
# docker restart d7db4d7c6499 d7db4d7c6499 # docker ps ID IMAGE COMMAND CREATED STATUS PORTS d7db4d7c6499 owncloud:latest /usr/sbin/apache2ctl 15 minutes ago Up 18 seconds 80->80
That’s hopefully given you a feel for Docker and the basics of how to get something up and running. At this point we have a very basic installation of Owncloud, there’s potentially a lot more to do before you’d consider making full-time use of it, such as updating the Apache httpd configuration to enable TLS and adding MySQL into the mix instead of SQLite as the database backend.
tl;dr – Feeling lazy?
What if you don’t care about creating your own image from scratch, you just want to be able to run an Owncloud instance with a couple of commands? From what I’ve described so far, this technology should be all about being able to do just that, right? Yup, of course – just do the following:
# docker pull yankcrime/owncloud
And subsequently spin up a new container from that image:
# docker run -d owncloud
Easy. Starting to understand the potential? (–:
Part 2 – adding SSL and MySQL into the mix – is online here.