1) The customer domain is normally not used as controlpanel login, instaed you use the domain of the hosting company. If you want to use the domains of your customers, then create a vhost in apache and redirect all incoming requests on port 8080 to the master.
2) The default server for new databases is set in the clients limits of the customer.
Also, on the second node, Roundcube is not working and crashes with Error 500 everytime. HTTP logs show no sign of a problem. Is it just me or is this normal?
There must be something in the global apache error.log.