HVM gives the best performance because you can take advantage of certain hardware features through the hypervisor. It's basically more direct access to the hard

HVM gives the best performance because you can take advantage of certain hardware features through the hypervisor. It's basically more direct access to the hardware, which makes it faster as you don't have as much hypervisor overhead. Amazon's "enhanced" networking and SSDs need HVM to get a good chunk of performance. Yes you'd have to build new AMIs with HVM. It'd be easiest if you had some kind of configuration management so you didn't need as many AMIs baked. When I build machines I use a script to handle the creation and mounting any extra volumes on a machine that I have as "nonstandard". I have only 2 custom AMIs - one for PV and the other for HVM. You'll need to have at least both, because if you wanted to use certain instances (t1.micro, m1.small come to mind) you can only use PV.