Adding support for building a rails image with the app directory mounted as a shared mount

onbuild/Dockerfile

@@ -8,12 +8,13 @@ WORKDIR /usr/src/app
 
 ONBUILD COPY Gemfile /usr/src/app/
 ONBUILD COPY Gemfile.lock /usr/src/app/
-ONBUILD RUN bundle install
 
 ONBUILD COPY . /usr/src/app
 
 RUN apt-get update && apt-get install -y nodejs --no-install-recommends && rm -rf /var/lib/apt/lists/*
 RUN apt-get update && apt-get install -y mysql-client postgresql-client sqlite3 --no-install-recommends && rm -rf /var/lib/apt/lists/*
 
 EXPOSE 3000
+COPY ./entrypoint.sh  /
+ENTRYPOINT [ "/entrypoint.sh"]
 CMD ["rails", "server", "-b", "0.0.0.0"]

onbuild/entrypoint.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+[ "$RUN_BUNDLE_INSTALL" == "false" ] || bundle install
+[ "$RUN_MIGRATIONS" == "true" ] && rake db:migrate
+[ "$RUN_DB_SETUP" == "true" ] && rake db:setup
+[ -n "$RUN_INIT_SCRIPT" ] && $RUN_INIT_SCRIPT
+
+exec "$@"