Multi-stage Dockerfile for Rails 5.2

.dockerignore

.git
.gitignore
Dockerfile
log
tmp
public/system

Dockerfile

FROM ruby:2.6.3-alpine3.9 AS base
RUN apk --update add tzdata postgresql-dev libxslt-dev libxml2-dev imagemagick
WORKDIR /app

# bundle install
FROM base as bundler

RUN apk --update add build-base
WORKDIR /app

COPY Gemfile Gemfile.lock ./
RUN echo 'gem: --no-rdoc --no-ri' > ~/.gemrc && \
    bundle install --no-cache --without development test --jobs 2

# build assets
FROM bundler AS assets
RUN apk --update add nodejs yarn
ENV RAILS_ENV=production
COPY config ./config
COPY package.json Rakefile ./
COPY app/assets ./app/assets
RUN SKIP_ALL_ROUTES=yes bundle exec rake assets:precompile

# final image
FROM base as final

ENV EXECJS_RUNTIME=Disabled RAILS_ENV=production

COPY --from=bundler /usr/local/bundle /usr/local/bundle
COPY --from=assets /app/public/assets ./public/assets

COPY . .

CMD ["/app/bin/rails", "server"]

routes.rb

Rails.application.routes.draw do
  return if ENV['SKIP_ALL_ROUTES']

  # ...
end