reworked things a bit:

-p option specifies the "main" or "admin" port. if you access this port without using a hostname
that's registered for an app (either through the web->url config setting, or using web->use_xip_io),
you'll get a welcome page listing all of the installed apps.

if you specify a port using web->port config setting, that port will be opened up and the app
will be served through that port.