title: Docker-Compose: Service xxx depends on service xxx which is undefined
body: <p>I'm having this error:</p>
  
  <blockquote>
    <p>ERROR: Service 'db' depends on service 'apache' which is undefined.</p>
  </blockquote>
  
  <p>Why is it saying that apache is undefined? I check the indentation. Should be the right one.</p>
  
  <pre><code>version: '3.5'
  
  services:
    apache:
      build: ./Docker
      image: apache:latest
      ports:
       - "80:80"
      restart: always
  networks:
         default:
           name: frontend-network
  
  services:
    db:
      image: mariadb:latest
      restart: always
      environment:
        MYSQL_ROOT_PASSWORD: example
      depends_on:
      - "apache"
    adminer:
      image: adminer
      restart: always
      ports:
      - "8080:8080"
      depends_on:
      - "db"
  networks:
        default:
          name: frontend-network
  </code></pre>