docker-compose.yml

# Asset compilation works by having the webpack container continually build an artifact,
# and that artifact being mounted for Rails to serve statically.
webpack:
  build: webpack/.
  command: npm run watch
  volumes:
    - ./webpack/config:/mnt/webpack/config
    - ./webpack/src:/mnt/webpack/src
    - ./volumes/webpack_build:/mnt/build
  # ...
  
rails:
  build: rails/
  working_dir: /mnt/rails
  volumes:
    - ./rails:/mnt/rails
    - ./volumes/webpack_build:/mnt/rails/public/webpack_build
  # ...