I have both, docker-compose.yml for backend and dockerfile for frontend. Backend depends on other services which themselve have their dockerfile. Neverthless, henrik proposed solution worked.
Thank your time @Firdaus
this means, instead of this: - traefik.http.routers.saralprod-saral-prod-b0moyj.rule=Host(api.saral.club) it should simply be - traefik.http.routers.saralprod-saral-prod-b0moyj.rule=Host(8000`)