If you prefer some other IaaS, fine. The point is that fabric can drive both the virtualization API and the actual set up of servers over SSH. I have a fake region called "dev" that runs the build against a vmware image on my local machine. It could work with Softlayer or Joyent or Rackspace or CloudFoundry or whatever.

Fabric and an IaaS provider is a really nice way to implement the PheonixServer pattern.