1. A network system for dynamically modifying the computer resources allocated to a virtual server, the network system comprising a plurality of physical hosts, the virtual server operating in a first physical host, the computer resources allocated to the virtual server being specified as a quality of service guarantee, the network system comprising: a virtual server resource monitor communicatively coupled to the first physical host and configured to monitor resource denials and to send a virtual server overloaded signal in response to the resource denials; a virtual server resource modifier communicatively coupled to the first physical host and configured to receive the virtual server overloaded signal and, in response to the virtual server overloaded signal, to modify a resource allocation for the virtual server and to send a virtual server resource modification signal; a load balancing module communicatively coupled to the plurality of physical hosts and configured to receive the virtual server resource modification signal and to determine whether the first physical host is overloaded and, in response to a determination that the first physical host is overloaded, to send a physical host transfer signal that indicates a second physical host; and a dynamic virtual server mover communicatively coupled to the plurality of physical hosts and configured to receive the physical host transfer signal and, in response to the physical host transfer signal, to transfer the virtual server from the first physical host to the second physical host.