nginx container fails to start if the rails container is not yet started
Since the docker legacy links were replace by docker networks, the nginx container may fail at startup (race condition) if the rails container is not yet up.
Allgo instance: backend qualif-rails:8080 frontend worker0.irisa.fr:443
nginx: [emerg] host not found in upstream "qualif-rails" in /etc/nginx/sites-enabled/default:97
nginx: configuration file /etc/nginx/nginx.conf test failed