Docker Ruby image based on Debian Wheezy

Dockerfile

FROM buildpack-deps:wheezy

RUN apt-get update && apt-get install -y curl procps && rm -rf /var/lib/apt/lists/*

ENV RUBY_MAJOR 2.1
ENV RUBY_VERSION 2.1.3

# some of ruby's build scripts are written in ruby
# we purge this later to make sure our final image uses what we just built
RUN apt-get update \
        && apt-get install -y bison ruby \
        && rm -rf /var/lib/apt/lists/* \
        && mkdir -p /usr/src/ruby \
        && curl -SL "http://cache.ruby-lang.org/pub/ruby/$RUBY_MAJOR/ruby-$RUBY_VERSION.tar.bz2" \
                | tar -xjC /usr/src/ruby --strip-components=1 \
        && cd /usr/src/ruby \
        && autoconf \
        && ./configure --disable-install-doc \
        && make -j"$(nproc)" \
        && apt-get purge -y --auto-remove bison ruby \
        && make install \
        && rm -r /usr/src/ruby

# skip installing gem documentation
RUN echo 'gem: --no-rdoc --no-ri' >> "$HOME/.gemrc"

# install things globally, for great justice
ENV GEM_HOME /usr/local/bundle
ENV PATH $GEM_HOME/bin:$PATH
RUN gem install bundler \
        && bundle config --global path "$GEM_HOME" \
        && bundle config --global bin "$GEM_HOME/bin"

# don't create ".bundle" in all our apps
ENV BUNDLE_APP_CONFIG $GEM_HOME

CMD [ "irb" ]

Based on upstream Docker Ruby image, but build on Debian Wheezy as opposed to Debian Jessie.