Pelican Blogging with a Docker Container
########################################

:title: Pelican Blogging with a Docker Container
:date: 2015-12-02
:category: Software
:tags: programming, docker, virtualisation, blogging
:slug: pelican-blogging-with-a-docker-container
:author: Chris Ramsay
:status: published
:language: en
:show_source: True

.. role:: bash(code)
   :language: bash

.. contents::

Current Virtual Server
----------------------

.. PELICAN_BEGIN_SUMMARY

It has been about a year since I started using a virtual server on the laptop
to locally host my blogging efforts with `Pelican`_. Up to now I have used a
combination of `Vagrant`_ (with Virtualbox in the background) and a `Puppet`_
built CentOS VM. At work we are increasingly introducing the concept of
containerised services in the form of `Docker`_ containers, and I felt that
revisiting my blogging setup with a view to making use of a container would be
a great way of getting to know the technology a little better.

.. PELICAN_END_SUMMARY

From Vagrant to Docker
----------------------

I should begin by stating that, although you will frequently see the question
"What is better, Docker or Vagrant?", it is not really a fair comparison. The
two technologies fulfil different use cases and overlap only in a minimal way.

Vagrant is generally more focused on providing a complete development
environment, therefore your Vagrant box might provide a web server and a
database within the same box.

Docker is an application oriented virtual environment with the Docker container
only providing what is absolutely necessary for the application to run, for
example just a web server. Should you require a database then that would be
provided by a separate Docker container.

So essentially, I am moving from a virtual machine focused on providing a whole
system to one that provides only bare essentials for getting the job done.

Getting Started with Docker
---------------------------

As there are hundreds of guides out there on how to install and get going with
Docker, I am not going to repeat my experience for you. Probably the most
helpful thing I could do would be to go ahead and deconstruct my *Dockerfile*,
so here goes.

This container is based on a clean `Debian`_ linux distribution. The *latest*
tag indicates that this will be latest stable release (*debian:jessie* at the
time of writing this). The *MAINTAINER* field is just metadata indicating who
the author is; quite self explanatory really!

.. code-block:: bash

    FROM debian:latest
    MAINTAINER Chris Ramsay <chris@ramsay-family.net>

This next block below gets the machine to run a general software update and in
addition install some basic requirements: Python, pip (which is a Python package
manager) and some development tools; those tools are purely to assist in
building some of the packages later.

.. code-block:: bash

    # Update & add prerequisites
    RUN apt-get -y update && apt-get install -y \
      python \
      python-dev \
      python-pip \
      git

Now that all the Python prerequisites are in place it is time to go ahead and
add the packages that will be required for Pelican, some of the Pelican plugins
and the build and deployment process, which I orchestrate using the `Fabric`_
Python library. Note that I also include a custom :bash:`.bashrc` file so that
I can give the terminal a nice command prompt and some handy aliases.

.. code-block:: bash

    WORKDIR /srv
    ADD requirements.txt /srv/requirements.txt
    ADD files/bashrc /root/.bashrc

Separately, the :bash:`requirements.txt` file that is brought in by the
:bash:`ADD` command looks like this:

.. code-block:: bash

    Fabric
    Jinja2
    Markdown
    MarkupSafe
    Pygments
    Unidecode
    argparse
    beautifulsoup4
    blinker
    docutils
    ecdsa
    feedgenerator
    paramiko
    pelican
    pycrypto
    python-dateutil
    pytz
    six
    smartypants
    typogrify
    wsgiref

Below, the final block uses Python's :bash:`pip` package manager to install the
packages from the requirements file above:

.. code-block:: bash

    RUN pip install -r requirements.txt

So if we have got here successfully it means that it is time to move a bunch of
files to the right place in the container OS in order to allow us to be able to
securely commit code changes to remote `git repositories`_
and `digitally sign commits`_ using `GNUPG`_. All these important files are
never stored in the Docker image itself as they would become available to
anyone with the ability to download my images and run Docker. In order to make them accessible to the Docker instance they are mounted in at run time from the
host machine:

.. code-block:: bash

    -v $wd/git/.gitconfig:/root/.gitconfig \
    -v $wd/gnupg:/root/.gnupg \
    -v $wd/ssh:/root/.ssh \

The three volume mount commands take place in a handy little script as
described in the next section. That is pretty all there is to it; just the most
basic things that I need to spend happy hours playing with the blog.

Up and Running
--------------
I have created a small shell script for when it comes to actually running the
container; it looks something like this:

.. code-block:: bash

    #!/bin/bash

    ###
    # Add more mounts for your projects after the git/gnupg/ssh ones
    # e.g. -v ~/stuff/myproject:/project \

    wd=$(pwd)
    docker rm -f pelicanbox
    docker run \
    --name pelicanbox \
    -p 80:8000 \
    -v $wd/git/.gitconfig:/root/.gitconfig \
    -v $wd/gnupg:/root/.gnupg \
    -v $wd/ssh:/root/.ssh \
    -v ~/work/blog:/project \
    -v ~/extras/pelican-plugins:/project/pelican-plugins  \
    -v ~/extras/pelican-themes:/project/pelican-themes \
    -ti \
    chrisramsay/docker-pelicanbox:latest \
    /bin/bash

The script above just saves me the hassle of having to remember what to type
on the command line each time. Once I am logged into the container, I just
navigate to the build directory and run the command to serve the site over
HTTP, then point the browser to (in my case) 192.168.99.100.

This is the End...
------------------

In summation, my early days with Docker have gone well and it is beginning to
prove itself to be a lightweight replacement for the Vagrant boxes I used to
run. As a bonus I have found that my laptop battery is lasting longer too!

.. footnotes

.. links

.. _`Pelican`: http://blog.getpelican.com/
.. _`Vagrant`: https://www.vagrantup.com/
.. _`Puppet`: https://puppetlabs.com/
.. _`Docker`: https://www.docker.com/
.. _`Debian`: https://hub.docker.com/_/debian/
.. _`Fabric`: http://www.fabfile.org/
.. _`git repositories`: https://git-scm.com/
.. _`digitally sign commits`: https://git-scm.com/book/en/v2/Git-Tools-Signing-Your-Work
.. _`GNUPG`: https://www.gnupg.org/