Ruby on Rails in Alpine Docker container

Dockerfile

# syntax = docker/dockerfile:1

# Make sure RUBY_VERSION matches the Ruby version in .ruby-version and Gemfile
ARG RUBY_VERSION=3.3.0
FROM registry.docker.com/library/ruby:$RUBY_VERSION-alpine as base

# Rails app lives here
WORKDIR /rails

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

# Install packages needed to build gems and deploy the application
RUN apk update && \
  apk add --no-cache bash libc6-compat tzdata


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

# Install packages needed to build gems
RUN apk add --no-cache build-base git postgresql-dev vips-dev pkgconf

# 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 apk add --no-cache curl vips postgresql-client && \
  rm -rf /var/cache/apk/*

# 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 adduser -D -s /bin/bash rails && \
  chown -R rails:rails db log storage tmp
USER rails:rails

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

# Start the server by default, this can be overwritten at runtime
EXPOSE 3000
CMD ["./bin/rails", "server"]