Ruby on Rails deployment Dockerfile

Dockerfile

# This multi-stage Dockerfile will use the full ruby image during build phase
# after this it wil build the deployment image based on the slim ruby container,
# copying over all artifacts from the build phase.
#
# The deployer image will not include a Javascript runtime and will come in at
# under 200MB for an average Rails application.

ARG BUILDER_FROM_IMAGE=ruby:3.0
ARG DEPLOY_FROM_IMAGE=ruby:3.0-slim
ARG NODE_VERSION 14.15.4
ARG YARN_VERSION 1.22.5

FROM $BUILDER_FROM_IMAGE as builder

# Install Node and Yarn

RUN set -ex \
    && for key in \
      94AE36675C464D64BAFA68DD7434390BDBE9B9C5 \
      FD3A5288F042B6850C66B31F09FE44734EB7990E \
      71DCFD284A79C3B38668286BC97EC7A07EDE3FC1 \
      DD8F2338BAE7501E3DD5AC78C273792F7D83545D \
      C4F0DFFF4E8C1A8236409D08E73BC641CC11F4C8 \
      B9AE9905FFD7803F25714661B63B535A4C206CA9 \
      77984A986EBC2AA786BC0F66B01FBB92821C587A \
      8FCCA13FEF1D0C2E91008E09770F7A9A5AE15600 \
      4ED778F539E3634C779C87C6D7062848A1AB005C \
      A48C2BEE680E841632CD4E44F07496B3EB3C1762 \
      B9E2F5981AA6E0CD28160D9FF13993A75599653C \
    ; do \
      gpg --batch --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys "$key" || \
      gpg --batch --keyserver hkp://ipv4.pool.sks-keyservers.net --recv-keys "$key" || \
      gpg --batch --keyserver hkp://pgp.mit.edu:80 --recv-keys "$key" ; \
    done \
    && curl -fsSLO --compressed "https://nodejs.org/dist/v$NODE_VERSION/node-v$NODE_VERSION-linux-x64.tar.xz" \
    && curl -fsSLO --compressed "https://nodejs.org/dist/v$NODE_VERSION/SHASUMS256.txt.asc" \
    && gpg --batch --decrypt --output SHASUMS256.txt SHASUMS256.txt.asc \
    && grep " node-v$NODE_VERSION-linux-x64.tar.xz\$" SHASUMS256.txt | sha256sum -c - \
    && tar -xJf "node-v$NODE_VERSION-linux-x64.tar.xz" -C /usr/local --strip-components=1 --no-same-owner \
    && rm "node-v$NODE_VERSION-linux-x64.tar.xz" SHASUMS256.txt.asc SHASUMS256.txt \
    && ln -s /usr/local/bin/node /usr/local/bin/nodejs

RUN set -ex \
  && for key in \
    6A010C5166006599AA17F08146C2130DFD2497F5 \
  ; do \
    gpg --batch --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys "$key" || \
    gpg --batch --keyserver hkp://ipv4.pool.sks-keyservers.net --recv-keys "$key" || \
    gpg --batch --keyserver hkp://pgp.mit.edu:80 --recv-keys "$key" ; \
  done \
  && curl -fsSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz" \
  && curl -fsSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz.asc" \
  && gpg --batch --verify yarn-v$YARN_VERSION.tar.gz.asc yarn-v$YARN_VERSION.tar.gz \
  && mkdir -p /opt \
  && tar -xzf yarn-v$YARN_VERSION.tar.gz -C /opt/ \
  && ln -s /opt/yarn-v$YARN_VERSION/bin/yarn /usr/local/bin/yarn \
  && ln -s /opt/yarn-v$YARN_VERSION/bin/yarnpkg /usr/local/bin/yarnpkg \
  && rm yarn-v$YARN_VERSION.tar.gz.asc yarn-v$YARN_VERSION.tar.gz

# /app is where our app will live

WORKDIR /app

# Bundle

COPY Gemfile /app
COPY Gemfile.lock /app
RUN bundle install -j 4 --without development test

# Yarn packages

COPY package.json /app
COPY yarn.lock /app
RUN yarn install --prod

# Copy app

COPY . /app

# Compile webpack assets

RUN RAILS_ENV=production SECRET_KEY_BASE=1 rails webpacker:compile && ln -s /app/public/packs /app/public/packs-test

# Build our final deployment image

FROM $DEPLOY_FROM_IMAGE AS deploy

WORKDIR /app
ENV RAILS_ENV=production RUBYOPT=-W:no-deprecated RAILS_LOG_TO_STDOUT=1

# Alternatively, set rails as entrypoing

CMD ["rails", "server"]

# Install runtime dependencies

RUN set -ex; \
	apt-get update; \
  apt-get install -y --no-install-recommends \
    libpq5 libjemalloc2 imagemagick \
  ; rm -rf /var/lib/apt/lists/*

# Use jemalloc to save some memory usage

ENV LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2

# Run as a non-priviledged user

RUN groupadd --gid 32767 rails \
  && useradd -s /bin/bash --uid 32767 --gid 32767 -m rails \
  && chown -R rails:rails /app

USER 32767

# Copy over app, bundle and assets

COPY --chown=32767:32767 . /app/
COPY --from=builder --chown=32767:32767 /usr/local/bundle /usr/local/bundle
COPY --from=builder --chown=32767:32767 /app/public/ /app/public/

# Done!

Running CI tests on the deployment image is easy, simply execute a bundle install --with test in the container before running your tests to create a correct build-test-deploy pipeline.