Dockerfile

# syntax=docker/dockerfile:1

# Make sure RUBY_VERSION matches the Ruby version in .ruby-version and Gemfile
ARG RUBY_VERSION=3.3.1
FROM registry.docker.com/library/ruby:$RUBY_VERSION-slim as base

WORKDIR /rails

# Set production environment
ENV RAILS_ENV="production" \
    BUNDLE_DEPLOYMENT="1" \
    BUNDLE_JOBS="4" \
    BUNDLE_WITHOUT="development:test" \
    BUNDLE_PATH="/usr/local/bundle"


# Throw-away build stage to reduce size of final image
FROM base as build

# Install packages needed to build gems
# NOTE: This example project intentionally does not require or install node.js

RUN --mount=type=cache,target=/var/cache/apt \
  --mount=type=cache,target=/var/lib/apt,sharing=locked \
  --mount=type=tmpfs,target=/var/log \
  rm -f /etc/apt/apt.conf.d/docker-clean; \
  echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' > /etc/apt/apt.conf.d/keep-cache; \
  apt-get update -qq \
  && apt-get install -yq --no-install-recommends \
    build-essential \
    gnupg2 \
    less \
    git \
    libpq-dev \
    libvips \
    pkg-config

# Install application gems
COPY Gemfile Gemfile.lock ./
RUN bundle install && \
    rm -rf ~/.bundle/ "${BUNDLE_PATH}"/ruby/*/cache "${BUNDLE_PATH}"/ruby/*/bundler/gems/*/.git && \
    bundle exec bootsnap precompile --gemfile

# Copy application code
COPY . .

# Precompile bootsnap code for faster boot times
RUN bundle exec bootsnap precompile app/ lib/

# Precompiling assets for production without requiring secret RAILS_MASTER_KEY
RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile


# Final stage for app image
FROM base

# Install packages needed for deployment
RUN --mount=type=cache,target=/var/cache/apt \
  --mount=type=cache,target=/var/lib/apt,sharing=locked \
  --mount=type=tmpfs,target=/var/log \
  rm -f /etc/apt/apt.conf.d/docker-clean; \
  echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' > /etc/apt/apt.conf.d/keep-cache; \
  apt-get update -qq \
  && apt-get install -yq --no-install-recommends \
  curl \
  postgresql-client \
  libvips

# Copy built artifacts: gems, application
COPY --from=build /usr/local/bundle /usr/local/bundle
COPY --from=build /rails /rails

# Run and own only the runtime files as a non-root user for security
RUN useradd rails --create-home --shell /bin/bash && \
    chown -R rails:rails db log storage tmp
USER rails:rails

# Entrypoint prepares the database.
ENTRYPOINT ["/rails/bin/docker-entrypoint"]

HEALTHCHECK --interval=15s --timeout=3s --start-period=0s --start-interval=5s --retries=3 \
  CMD curl -f http://localhost:3000/up || exit 1

# Start the server by default, this can be overwritten at runtime
EXPOSE 3000
CMD ["bundle", "exec", "puma", "-C", "config/puma.rb"]