Been trying to follow the instructions in this person's github to set up nextcloud on a brand new domain 0x63.xyz. Using a reverse proxy with traefik 2 to set up containers to run under their respective subdomains. Traefik seems to run okay on port 8080 but when I try to go to the nextcloud subdomain I get a Gateway Timeout error. Some Googling seems to suggest that this means nextcloud isn't on the same network as traefik, but it's on the webproxy network created by traefik (I think). My configs are at https://gist.github.com/c-kirkeby/1abea52c1028fbbdcae373565b31c776 with passwords redacted.
Traefik does not create any networks.
You have to create the networks yourself.
Also, if your containers use multiple networks, you need to set the network for Traefik to use (https://docs.traefik.io/v2.1/providers/docker/#network) so that it uses the correct IP.
That should allow Traefik to communicate with your container.