title: Docker Compose File cant get .env Variables
body: <p>I am using docker-compose to run a traefik container. The Domain of this Container should be set by an environment file but everytime i start this service it says:</p>
  
  <p>WARNING: The DOMAIN variable is not set. Defaulting to a blank string</p>
  
  <p>My compose-file setup:</p>
  
  <pre><code>version: '3.5'
  
  networks:
    frontend:
      name: frontend
    backend:
      name: backend
  
  services:
    Traefik:
      image: traefik:latest
      command: --api --docker --acme.email="test@test.de"
      restart: always
      container_name: Traefik
      networks:
        - backend
        - frontend
      env_file: ./env.env
      volumes:
        - /var/run/docker.sock:/var/run/docker.sock
        - ./traefik/traefik.toml:/traefik.toml
        - ./traefik/acme.json:/acme.json
      ports:
        - "80:80"
        - "443:443"
      labels:
        - "traefik.docker.network=frontend"
        - "traefik.enable=true"
        - "traefik.frontend.rule=Host:traefik.${DOMAIN}"
        - "traefik.port=8080"
        - "traefik.protocol=http"
  </code></pre>
  
  <p>My env.env file setup:</p>
  
  <pre><code>DOMAIN=fiture.de
  </code></pre>
  
  <p>Thanks for your Help!</p>