Sorry for the mixed-up title, but let me try to explain better:

We run a hosting solution, which until now has supported shared hosting and VPSes. Easy enough.

We are now getting larger clients which require a more complex setup. We have more or less settled the server-setup itself, which will consist of:

• 1-2 Frontend Proxy/Load balancing servers
• 2+ Application servers
• 1 Database server
• 1 optional Memcached server

The issue we are dealing with is to agree on a flexible and easy-to-maintain IP setup. So far we've been into VLAN'ing the internal servers in its own subnet, we've though of assigning an official IP to each server, and so on.

What will be the best approach here? Any best practices? Using one official IP on the Frontend server, and then just set up an internal subnet for the servers behind that?

We could then just NAT in any eventual sources required to access for instance the DB server directly over 3306.