Rancher HA cluster, adding custom hosts

Hello, i’m trying to set up a Rancher HA cluster. I have 3 docker hosts with the Rancher agent installed on each one.
I have an external server with mysql installed that they use. It also has nginx installed pointing my rancher.domain.com to the 3 hosts to loadbalance the UI.

If i try using the same url to add a host to my cluster it never shows up in Rancher…
What kind of configuration do i need for my loadbalancer to work when adding hosts?