Currently I'm running a production server with ISPConfig 3. The OS is Debian-Lenny, and it's configured as described by Falko in 'The perfect server - Debian Lenny'. Now I want to set up a separate web server (as ISPConfig slave) and move the web sites to that server. All other services (mail, DNS) will remain on the old server. Both servers will have their own public IP address. What is the best way to move the web sites with as least downtime as possible?