for CUPS 2.4.12-0ubuntu1.1
when adding to cupsd.conf a ServerAlias of the type below, it doesn't acknowledge it.

ServerName localhost
ServerAlias localhost
ServerAlias cups.customer.com

in error_log with debug mode enabled I'm only getting:
D [...] Added auto ServerAlias localhost

I need to make CUPS available for printing purposes only over a public LBaaS.