CrushFTP supports high availability mode for Enterprise licenses.
This mode will allow for multiple servers to have *Replication* between the servers. A client is valid on all servers, as long as they stick to the server they started on.
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. A single Internal server can manage multiple DMZ servers., But only one internal server should be connected to a DMZ instance, they cannot be cross linked.