nginx config requires base service name to be app

[Pingumania]

I have multiple services in one docker-compose file, for easier readability I renamed blackcandy from app to blackcandy.

blackcandy: &blackcandy_base
    image: blackcandy/blackcandy
    container_name: blackcandy_app
    networks:
      - internal
    volumes:
      - /mnt/share/audio/musik:/media_data:ro
      # - production_uploads_data:/app/public/uploads
    environment:
      DB_HOST: blackcandy_postgres
      DB_USER: postgres
      REDIS_CACHE_URL: redis://blackcandy_redis:6379/1
      REDIS_SIDEKIQ_URL: redis://blackcandy_redis:6379/2
      MEDIA_PATH: /media_data
    depends_on:
      - blackcandy_postgres
      - blackcandy_redis

  blackcandy_postgres:
    image: postgres:11.1-alpine
    container_name: blackcandy_postgres
    networks:
      - internal
    volumes:
      - $DOCKERDIR/postgres/blackcandy:/var/lib/postgresql/data

  blackcandy_redis:
    container_name: blackcandy_redis
    networks:
      - internal
    image: redis:4.0-alpine

  blackcandy_worker:
    <<: *blackcandy_base
    container_name: blackcandy_worker
    command: bundle exec sidekiq

  blackcandy_web:
    <<: *blackcandy_base
    container_name: blackcandy_web
    networks:
      - internal
      - proxy
    depends_on:
      - blackcandy
      - blackcandy_worker
    command: nginx -g 'pid /tmp/nginx.pid; daemon off;'
    labels:
      traefik.enable: true
      traefik.http.routers.blackcandy.entrypoints: web-secure
      traefik.http.routers.blackcandy.rule: Host(`blackcandy.$DOMAINNAME`)
      traefik.http.services.blackcandy.loadbalancer.server.port: 80
      traefik.http.services.blackcandy.loadbalancer.server.scheme: http

Here is the error I get:

mb@dockerhost:~$ docker logs blackcandy_web
nginx: [emerg] host not found in upstream "app:3000" in /etc/nginx/nginx.conf:19

Not a huge deal but maybe we can change this via an environment variable?