A minimal debian based Docker container with Ruby and Bundler installed.
Version tags are based off the installed Ruby version
Before the official language stacks most 'language' images just had too much junk in them. I wanted something small(ish) and basic. The language stacks are awesome, no doubt, however I found that we still needed to install a bunch of things for our gems and I wanted to use arbitrary Ruby versions. So, there you have it.
Edit the Dockerfile to use the version of Ruby you need.
Build the container, and tag it with the Ruby version
$ docker build -t='yourname/ruby:_version_'
Set up your Dockerfile to use this image
# in your Dockerfile
FROM yourname/ruby:_version_
...
Then build away!