We can use variables in our docker-compose.yml files!

The syntax is: ${SOME_VAR_NAME}.

These specifically are environment variables.

First, let's set our docker-compose.yml file to read two variables:

version: '3'
services:
  app:
    build:
      context: ./docker/app
      dockerfile: Dockerfile
    image: shippingdocker/app:latest
    networks:
     - appnet
    volumes:
     - .:/var/www/html
    ports:
     - ${APP_PORT}:80
    working_dir: /var/www/html
  cache:
    image: redis:alpine
    networks:
     - appnet
    volumes:
     - cachedata:/data
  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: homestead
      MYSQL_USER: homestead
      MYSQL_PASSWORD: secret
    ports:
     - ${DB_PORT}:3306
    networks:
     - appnet
    volumes:
     - dbdata:/var/lib/mysql
  node:
    build:
      context: ./docker/node
      dockerfile: Dockerfile
    image: shippingdocker/node:latest
    networks:
     - appnet
    volumes:
     - .:/opt
    working_dir: /opt
    command: echo hi
networks:
  appnet:
    driver: bridge
volumes:
  dbdata:
    driver: local
  cachedata:
    driver: local

We have APP_PORT and DB_PORT.

We can set those in two ways:

First: We can export the variables so they're available to sub-processes:

export APP_PORT=8080
export DB_PORT=33060

# Our `docker-compose.yml` file will use the above variables
docker-compose up -d

Second: We can set them inline as we run the docker-compose command.

APP_PORT=8080 DB_PORT=33060 docker-compose up -d

.env File

We have another option too! Docker Compose will read a .env file and import variables from it!

Here's an example .env file:

APP_PORT=8080
DB_PORT=33060

If that's in the same directory as the docker-compose.yml file, then we can just run docker-compose commands, knowing it will pick up those variables:

docker-compose up -d