How route a domain to another backend?

Traefik Traefik v1
8

I'll throw in my docker-compose as well so you got it all:

version: '3.7'
services:

    traefik:
        image: traefik:v1.7.14-alpine
        container_name: traefik
        restart: always
        networks:
            - web
        ports:
            - 80:80
            - 443:443
            - 8080:8080
        volumes:
            - /var/run/docker.sock:/var/run/docker.sock:ro
            - /home/ladmin/docker/traefik/traefik.toml:/traefik.toml
            - /home/ladmin/docker/traefik/acme.json:/acme.json
        environment:
            - CF_API_EMAIL=${CLOUDFLARE_EMAIL}
            - CF_API_KEY=${CLOUDFLARE_API_KEY}
        labels:
          - 'traefik.port=8080'
          - 'traefik.docker.network=web'
          - 'traefik.enable=true'
          - 'traefik.frontend.rule=Host:dash.localhost,dash.${DOMAINNAME}'

    grillgeek:
        image: swemattias/grillgeek
        container_name: grillgeek
        restart: always
        networks:
            - web
            - default
        expose:
            - 80
        labels:
            - 'traefik.docker.network=web'
            - 'traefik.enable=true'
            - 'traefik.frontend.rule=Host:${DOMAINNAME},www.${DOMAINNAME}'

    whoami:
        image: jwilder/whoami
        expose:
            - 8000
        labels:
            - 'traefik.docker.network=web'
            - 'traefik.enable=true'
            - 'traefik.frontend.rule=Host:whoami.${DOMAINNAME}'

    ombi:
        image: linuxserver/ombi
        container_name: ombi
        environment:
            - PUID=1000
            - PGID=1000
            - TZ=Europe/Stockholm
            - BASE_URL=ombi.grillgeek.se
        volumes:
            - ./ombi/:/config
        ports:
            - 3579:3579
        restart: unless-stopped
        labels:
            - 'traefik.docker.network=web'
            - 'traefik.enable=true'
            - 'traefik.frontend.rule=Host:ombi.${DOMAINNAME}'


#    sundsvallbbq:
#        image: swemattias/sundsvallbbq
#        container_name: sundsvallbbq
#        restart: always
#        networks:
#            - web
#            - default
#        expose:
#            - 80
#        labels:
#            - 'traefik.docker.network=web'
#            - 'traefik.enable=true'
#            - 'traefik.frontend.rule=Host:${DOMAINNAME2},www.${DOMAINNAME2}'

networks:
    web:
        external: true

As you can see I added Ombi, just to try, since whoamI works, I thought, hey, I don't need to add all services via rules.toml. I added Ombi and it appears inside the dashboard all looks as well.
But visiting the url (which you can do your self) gives me a Gateway timeout.
Visiting host-ip:3579 works just fine.

How hard can this be to get correct?