Just adding on to this in case this is not obvious. You will have to expose an endpoint of Dgraph Alpha HTTP(S) service. On a production scenario, this should never be accessible, so you would then need to go through an SSH jump host or a VPN to access a private internal-facing LB that hits the Dgraph Alpha service.
The Ratel is only a client, so it can run on a laptop, or if desired, from the private network as well. If
you can run curl https://alpha.example.com:8080/health (replace FQDN to IP or hostname you are using) works fine, then the same address will work with Ratel’s connection configuration.