Nimbus is an open-source toolkit that, once installed on a cluster, provides an infrastructure as a Servicecloud to its client via WSRF-based or Amazon EC2WSDLweb serviceAPIs. Nimbus supports the Xen hypervisor and virtual machine schedulers PBS and SGE. It allows deployment of self-configured virtual clusters via contextualization. It is configurable with respect to scheduling, networking leases, and usage accounting.