The reverse proxy should work
It complains about invalid domain
I have setup pihole on a raspbian image on an RPi2 and added VIRTUAL_HOST=pihole.domain.com to /etc/environment.
The traefik server is on a different machine and is set up to just do ssl termination and reverse-proxy to the ip of the rpi2 at port 80. Either pihole does not get the environment variable or something else is broken here.
Thanks in advance