Usher: an extensible framework for managing custers of virtual machines

Usher is a virtual machine management system designed to impose few constraints upon the computing environment under its management. Usher enables administrators to choose how their virtual machine environment will be configured and the policies under which they will be managed. The modular design of Usher allows for alternate implementations for authentication, authorization, infrastructure handling, logging, and virtual machine scheduling. The design philosophy of Usher is to provide an interface whereby users and administrators can request virtual machine operations while delegating administrative tasks for these operations to modular plugins. Usher's implementation allows for arbitrary action to be taken for nearly any event in the system. Since July 2006, Usher has been used to manage virtual clusters at two locations under very different settings, demonstrating the flexibility of Usher to meet different virtual machine management requirements.