Dockerfile: multi-stage

Dockerfile

# ---- Base Node ----
FROM ubuntu AS base
# install the core dependencies
RUN apt-get install -y my package list
# set working directory
WORKDIR /app
# copy project file
COPY Gemfile .
COPY Gemfile.lock

# ---- Dependencies ----
FROM base AS dependencies
# install dependencies
RUN bundle install --without development test
 
# ---- Test ----
# run linters, setup and tests
FROM dependencies AS test
COPY . .
RUN  bundle install --without development && rspec

# ---- Release ----
FROM base AS release
# copy production node_modules
COPY --from=dependencies gems ./gems
# copy app sources
COPY . .
# expose port and define CMD
EXPOSE 5000
CMD ["app", "start"]