You can have multiple Forms servers connect to same database: for example, one in internal and one in DMZ. Each Forms server have a web application called "FormsAppPool" and a windows service called "Laserfiche Forms Routing Service", the Laserfiche Forms Routing Service need to talk to the primary Forms Server web site to get the resources such as the submitted form to generate pdf when save to repository and it will send email notification to the end users with link to the user task(it will use the Forms Server Primary URL in the link), that's the reason "you must specify a primary Forms server that can be accessed by the routing service and users for each other Forms server."