1. A computer system for implementing an application topology on a host computer as virtual machines, comprising: a topology store that stores a topology that includes, for each computer represented by the topology, an indication of a network to which the computer is connected and an indication of applications that are associated with the computer; a create topology component that executes on the host computer and, for each computer of the topology, creates, configures, and launches a virtual machine in accordance with the topology; and an initialize virtual machine component that executes when a virtual machine is launched and initializes applications in accordance with the topology.