Dockerfile

# syntax = docker/dockerfile:1

# Make sure RUBY_VERSION matches the Ruby version in .ruby-version and Gemfile
ARG RUBY_VERSION=3.3.6
FROM ruby:$RUBY_VERSION-slim AS base

ARG GIT_SHA
ENV GIT_SHA=${GIT_SHA:-unknown}

# Rails app lives here
WORKDIR /rails

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

# Update gems and bundler
RUN gem update --system --no-document && \
    gem install -N bundler


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

# Install packages needed to build gems
RUN --mount=type=cache,id=dev-apt-cache,sharing=locked,target=/var/cache/apt \
    --mount=type=cache,id=dev-apt-lib,sharing=locked,target=/var/lib/apt \
    apt-get update -qq && \
    apt-get install --no-install-recommends -y build-essential git

# Install application gems
COPY --link Gemfile Gemfile.lock .ruby-version ./
RUN --mount=type=cache,id=bld-gem-cache,sharing=locked,target=/srv/vendor \
    bundle config set app_config .bundle && \
    bundle config set path /srv/vendor && \
    bundle install && \
    bundle exec bootsnap precompile --gemfile && \
    bundle clean && \
    mkdir -p vendor && \
    bundle config set path vendor && \
    cp -ar /srv/vendor .

# Copy application code
COPY --link . .

# 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,id=dev-apt-cache,sharing=locked,target=/var/cache/apt \
    --mount=type=cache,id=dev-apt-lib,sharing=locked,target=/var/lib/apt \
    apt-get update -qq && \
    apt-get install --no-install-recommends -y curl libjemalloc2

# 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 groupadd --system --gid 1000 rails && \
    useradd rails --uid 1000 --gid 1000 --create-home --shell /bin/bash && \
    chown -R 1000:1000 db log storage tmp
USER 1000:1000

ENV LD_PRELOAD="libjemalloc.so.2" \
    MALLOC_CONF="dirty_decay_ms:1000,narenas:2,background_thread:true"

# Entrypoint sets up the container.
ENTRYPOINT ["/rails/bin/docker-entrypoint"]

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