How to create an octopress docker image and publish it on DockerHub

December 24, 2015

This are my notes about how to configure a docker image and publish it on DockerHub. It's just a condensed guide but you won't find anything new.

As you know octopress is a ruby project with some peculiar dependency. I'm not a ruby developer so I would like not to have that many things on my pc used only for that purpose.

Now, my intention is to use this image as a virtual machine where I can run octopress commands. And that's not how you usually use a docker image. It's actually really different from the day to day usage but I'm not going to argue about the fact that I'm not using it in the proper way: you're right and Han shot first. That is not going to change the fact that we had Episodes 1 2 and 3 and the same goes for how I use docker in this case.

(if you're wondering about the fact that all this ranting was to make a Star Wars reference: right again :P )

When you create a new image you'll describe the way it's configured in a Dockerfile. Let's see mine:

FROM debian:jessie
MAINTAINER Emanuele Ianni <dierre@gmail.com>

ENV BUILD_PACKAGES bash libcurl4-openssl-dev git
ENV RUBY_PACKAGES ruby ruby-dev bundler
ENV EXECJS_DEPENDENCY nodejs
ENV GIT_URL https://github.com/octopress/octopress.git

# Update and install all of the required packages.
# At the end, remove the apk cache
RUN apt-get update -y
RUN apt-get upgrade -y
RUN apt-get install -y $BUILD_PACKAGES
RUN apt-get install -y $RUBY_PACKAGES
RUN apt-get install -y $EXECJS_DEPENDENCY
RUN rm -rf /var/cache/apk/*

# cloning octopress repo and installing version

RUN gem install --no-rdoc --no-ri pry-byebug
RUN gem install --no-rdoc --no-ri octopress-ink
RUN gem install --no-rdoc --no-ri clash
RUN gem install --no-rdoc --no-ri octopress
RUN mkdir octopress
WORKDIR octopress

You can check official documentation to know how to use docker build and what keys you can user in a Dockerfile.

What I would like to stress about it here is just keep it readable because configuring a docker image could be really complex. You can use ENV to set up environment variables that you can use later with $VARIABLE. Remember the difference between RUN and CMD. RUN is used with docker build whereas CMD is used when you use docker run.

In this particular case to build the image (that you can find on DockerHub ) just run docker build -t octopress ..

To run it is a little bit trickier than usual but it's doable: docker run -p 4000:4000 -v /Users/dierre/Projects/octopress/:/octopress -i -t --entrypoint="/bin/bash" invasionofsmallcubes/octropress.

Here you expose the port 4000 that you will later use to check a preview of your blog, you'll start your docker image opening a console and then you share the content of your octopress repository that in my case is in /Users/dierre/Projects/octopress/.

To tag a built image you can just follow the official documentation, it's pretty straightforward.

Last note: if you are using OSX then docker will start in a VirtualBox machine named default which has a specific address. You you want to see a preview of the blog, remember to run jekyll serve --host 0.0.0.0, where the option --host 0.0.0.0 is used to open jekyll to answer to every call from everywhere, because the default behaviour is just listen to 127.0.0.1 which is not a viable solution when using docker since you are using the host browser.

I hope it's helpful.