Virtual machines of a virtual data center generate runtime instances with a software image, hardware configuration, management configuration and user/service configuration. Virtual data center resource use is monitored by reference to the management configuration of runtime instances, such as for environmental controls like power, cooling and balancing, or for policy limitations on users, software or hardware. Users or services generate runtime instances of stored virtual machines by reference to the user/service configuration, such as pricing or priority. In one example embodiment, the virtual machine software image comprises an application system preparation file that populates a read only application image common to plural virtual machines. Information unique to each virtual machine with respect to the application is maintained in the user/service configuration of the virtual machine and version information is maintained in the management configuration of the virtual machine. Updates to the application across each virtual machine are performed by updating the read only image or any of its configuration information for hardware configuration, management configuration or user/service configuration.