Docker compose example using volumes out of Dockerfile build context

docker-compose.yml

version: '3'
services:
  webserver:
    # using a custom image that we already bulit with 'docker build -t customimage .'
    image: customimage

    container_name: web

    # we want to sync the REQUIRED cms-public repo root folder with the container's public folder for the rails app
    volumes:
      - ../cms-public:/usr/src/app/public

    # expose ports for rails
    ports:
      - "3000:3000"

    working_dir: /usr/src/app