1. An article of manufacture including program logic for providing on-demand resource allocation in a cluster having at least one initial virtual machine, wherein the program logic causes operations to be performed, the operations comprising: determining that resource requirements have changed; creating at least one new virtual machine on at least one physical machine based on the changed resource requirements; adding the at least one new virtual machine to the initial cluster; and failing over transactions for the at least one initial virtual machine to the at least one new virtual machine.