My very first Dockerfile! It installs Ruby 2.0 from scratch, installs bundler, and then vendors in my app and installs dependencies.

Dockerfile

MAINTAINER Pete Keen "pete@petekeen.com"

# Use Ubuntu 12.04 as the base image
FROM ubuntu:precise

# Install a bunch of prerequisites
RUN apt-get update
RUN apt-get install -y git-core curl wget libssl1.0.0 python-yaml build-essential libssl-dev

# Install ruby-build
RUN git clone https://github.com/sstephenson/ruby-build.git
RUN cd ruby-build && ./install.sh
RUN mkdir -p /opt/rubies

# Install Ruby 2.0.0-p0
RUN /usr/local/bin/ruby-build 2.0.0-p0 /opt/rubies/2.0.0-p0
ENV PATH /app/bin:/app/vendor/bundle/bin:/opt/rubies/2.0.0-p0/bin:/usr/local/bin:/usr/bin:/bin
RUN gem install bundler

# Vendor in the app, in this case the directory where the Dockerfile is
ADD . /app

# Install app dependencies with bundler
RUN cd /app && bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin

Hi @peterkeen

Like the way you have this set up, later versions of Docker appear to be more strict on ordering, and require the FROM to come before the MAINTAINER