docker-compose.yml

version: '3.7'

services:
  mongo:
    # To create this service, Compose will pull the mongo
    image: mongo:4.2.5
    container_name: calamus_mongo
    restart: unless-stopped
    # This tells Compose that we would like to add environment variables 
    # from a file called .env, located in our build context.
    env_file: .env
    environment:
      # MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_ROOT_PASSWORD together create
      # a root user in the admin authentication database and ensure that authentication is enabled 
      # when the container starts. We have set MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_ROOT_PASSWORD 
      # using the values from our .env file, which we pass to the db service using the env_file option.
      - MONGO_INITDB_ROOT_USERNAME=$DB_ADMIN
      - MONGO_INITDB_ROOT_PASSWORD=$DB_ADMIN_PWD
      - MONGO_INITDB_DATABASE=$DB_NAME
    ports:
      - "$DB_PORT:27017"
    volumes:     
    - ./mongodb/init-mongo.js:/docker-entrypoint-initdb.d/init-mongo.js:ro
      # The named volume dbdata will persist the data stored in Mongo’s default data directory, /data/db. 
      # This will ensure that you don’t lose data in cases where you stop or remove containers.
    - dbdata:/data/db

# Our top-level volumes key defines the volumes dbdata. 
# When Docker creates volumes, the contents of the volume are stored in a part of the host filesystem, /var/lib/docker/volumes/, that’s managed by Docker. 
# The contents of each volume are stored in a directory under /var/lib/docker/volumes/ and get mounted to any container that uses the volume. 
# In this way, the data that our users will create will persist in the dbdata volume even if we remove and recreate the db container.
volumes:
  dbdata: