Example of rbdock, https://github.com/tcnksm/rbdock

Dockerfile

FROM ubuntu

# Install basic packages
RUN apt-get update
RUN apt-get install -y build-essential wget curl git
RUN apt-get install -y zlib1g-dev libssl-dev libreadline-dev libyaml-dev libxml2-dev libxslt-dev
RUN apt-get clean

# Install ruby-build
RUN git clone https://github.com/sstephenson/ruby-build.git .ruby-build
RUN .ruby-build/install.sh
RUN rm -fr .ruby-build

# Install ruby-2.1.0
RUN ruby-build 2.1.0 /usr/local

# Install bundler
RUN gem update --system
RUN gem install bundler --no-rdoc --no-ri