We currently host all of our clients in one datacenter. We would like to expand to two new datacenters by the end of the year. My job is to figure out how to extend our current network to those two locations.
I have some basic designs drawn up (site to site VPNs between the datacenters, OSPF for internal routing, round-robin DNS to distribute the load), but I could really use some advice from someone who has done this before. My major concern is making a design choice that will constrain us or require a redesign in the future. We already have some design choices that will hamper us in the future (e.g. every client gets their own 10.x.x.x/24 subnet with their own VLAN, which will work great right up until our 4093rd client).
Does anyone know some good resources on how to create a scalable network design?
EDIT: Our business resembles VPS hosting, so as you can imagine, there's all types of traffic. Most of it is web (80,443) and mail though, so throughput is the usual priority followed by latency.
The business reason we want to expand is so our clients can host their servers either on the East/West Coast US or South Pacific Asia. The IT reason is to give us a disaster recovery site in case of natural disaster.
EDIT 2: Just to be clear I'm looking for resources on how to design the network. The details on how to do it (VPNs, routing, DNS, etc.) I can do.