Split env file into multiple files

.env

REGISTRY_PATH=registry.domain.tld
TAG_PHP=7.2
TAG_NGINX=1.17.5
HTTP_PORT=2000
REPLICA_COUNT_PHP=3
REPLICA_COUNT_NGINX=3
DATABASE_NETWORK=mysql-005
NGINX_MEM_LIMIT=215M
PHP_MEM_LIMIT=2G
MEMORY_LIMIT=2G
HOSTNAME=domain.tld
DB_HOST=127.0.0.1
DB_PORT=3306
DB_NAME=test
DB_USER=root
DB_PASSWORD=very_sensitive_password

docker-compose.yml

version: '3.5'
services:
  # Php service configuration
  php:
    image: ${REGISTRY_PATH}/php:${TAG_PHP}
    env_file: .env
    networks:
      - default
      - database
    deploy:
      replicas: ${REPLICA_COUNT_PHP:-1}
      resources:
        limits:
          memory: "${PHP_MEM_LIMIT:-1G}"

  # Nginx service configuration
  nginx:
    image: ${REGISTRY_PATH}/nginx:${TAG_NGINX}
    env_file: .env
    networks:
      - default
    ports:
      - ${HTTP_PORT}:80
    deploy:
      replicas: ${REPLICA_COUNT_NGINX:-1}
      resources:
        limits:
          memory: "${NGINX_MEM_LIMIT:-1G}"

networks:
  default:
  # The database network is external because used by many docker stacks
  database:
    external: true
    name: "${DATABASE_NETWORK}"