1. A method for use in a system having plural physical machines that each contains one or more active virtual machines, comprising: receiving, at a load balancer, a request from a client; in response to the request, determining whether at least one additional virtual machine should be started up; in response to determining that at least one additional virtual machine should be started up, the load balancer sending at least one command to start up the at least one additional virtual machine in at least one of the physical machines; a placement controller modifying placement of the active virtual machines on the physical machines in response to starting up of the at least one additional virtual machine; computing by the placement controller indicators associated with corresponding plural different layouts of the active virtual machines and the at least one additional virtual machine on the physical machines; selecting, by the placement controller, one of the plural layouts based on the indicators; placement controller one of the plural layouts based on the indicators; determining, by the load balancer, whether a workload loading of the active virtual machines and the at least one additional virtual machine has fallen below a threshold; and in response to determining that the workload loading has fallen below the threshold, disabling a particular one of the active virtual machines and the at least one additional virtual machine.