We think of applications today as an executable sitting on a virtual machine,” said Forrester’s Kindness. “They may talk about two- or three-tiered applications, too, but when you move to the cloud, developers change the way they develop applications. When you move to Amazon Web Services, it’s your responsibility to create an application that can move around when a server goes down. That application executable is being broken up into multiple files on multiple servers, so if one goes down, another can come up and it can keep on going. Think about the way those applications go back and forth now. It changes the way networking is done, whether on the LAN or across the WAN. You have more traffic, but it will be smaller and more dispersed.
Nice summary from Andre Kindness.