This is an example application built from a dockerfile. It is a minimal Ruby Sinatra application that return the user's IP address when they visit the site.
The Dockerfile installs the system Ruby (v 1.9.3) associated with Ubuntu 14.04.
See https://registry.hub.docker.com/u/craic/docker_sinatra_example_2/ for the same application built from a Dockerfile which builds Ruby 2.1.2 from source.
All source code is available at https://github.com/craic/docker_sinatra_examples