Dockerfile

# Build compilation image
FROM ruby:2.7.2-alpine as builder

# The application runs from /app
WORKDIR /app

# Add the timezone as it's not configured by default in Alpine
RUN apk add --update --no-cache tzdata && \
  cp /usr/share/zoneinfo/Europe/London /etc/localtime && \
  echo "Europe/London" > /etc/timezone

# build-base: complication tools for bundle
# yarn: node package manager
# postgresql-dev: postgres driver and libraries
RUN apk add --no-cache build-base yarn postgresql-dev

# Install bundler to run bundle exec
# This should be the same version as the Gemfile.lock
RUN gem install bundler:2.1.4 --no-document
RUN bundle config set without 'development test'

# Install gems defined in Gemfile
COPY .ruby-version Gemfile Gemfile.lock /app/
RUN bundle install --jobs=4 --no-binstubs

# Install node packages defined in package.json, including webpack
COPY package.json yarn.lock /app/
RUN yarn install --frozen-lockfile

# Copy all files to /app (except what is defined in .dockerignore)
COPY . /app/

# Compile assets and run webpack
# Run in rails test environment to avoid loading development gems
RUN RAILS_ENV=test bundle exec rails assets:precompile

# Cleanup to save space in the production image
RUN rm -rf node_modules log tmp && \
      rm -rf /usr/local/bundle/cache && \
      rm -rf .env && \
      find /usr/local/bundle/gems -name "*.c" -delete && \
      find /usr/local/bundle/gems -name "*.h" -delete && \
      find /usr/local/bundle/gems -name "*.o" -delete && \
      find /usr/local/bundle/gems -name "*.html" -delete

# Build runtime image
FROM ruby:2.7.2-alpine as production

# The application runs from /app
WORKDIR /app

# Add postgres driver library
# Add the timezone as it's not configured by default in Alpine
RUN apk add --update --no-cache libpq tzdata && \
  cp /usr/share/zoneinfo/Europe/London /etc/localtime && \
  echo "Europe/London" > /etc/timezone

# Copy files generated in the builder image
COPY --from=builder /app /app
COPY --from=builder /usr/local/bundle/ /usr/local/bundle/