docker-development.yml

# allows for swarm mode
version: '3'

# provides development overrides to docker-compose.yml
services:
    web:
        environment:
            NODE_ENV: development
        volumes:
            # binds host's files to container's files (for quicker development cycles)
            - .:/app 
            # creates volume to store node_modules - Since npm install is only run when the image is built, 
            # the installed node_modules would exist in the image but not the host. In addition, the above 
            # binding mounts the host's files on top of the container's files. Therefore, because the host
            # does not have node_modules, this binding causes the container to ignore the node_modules that 
            # were installed in the image and instead, mimic the host's state. Having this volume forces the
            # container to use the node_modules from the docker image, overriding the bind's effects. 
            # (http://jdlm.info/articles/2016/03/06/lessons-building-node-app-docker.html)
            - /app/node_modules
        ports:
            - "3000:3000"