CrushFTP supports high availability mode for Enterprise licenses.  This mode will allow for multiple servers to share a clustered WebInterface session cache between the servers.  A client is valid on all servers, so if a load balancer directed the client to another server, their logged in session is still valid.

This can be combined with the [ServerBeat] feature to manage a Virtual IP between multiple machines.  This way incoming access points to the VIP, and that VIP will move to a machine that is operational in the event the current machine using the VIP goes down.

Lastly the [DMZ] mode can be used placing a DMZ server being controlled by internal an CrushFTP server separated by a firewall allowing only outgoing initiated connections.  There can be multiple DMZ servers controlled by one internal server, or multiple internal servers sharing in management of multiple DMZ servers.