NIST [3] has made e orts to provide a uni ed way to de ne cloud computing and its main functionality. Despite its complexity and heterogeneous nature, NIST has identi ed ve essential characteristics that represent a cloud computing platform:• On-demand self-service: Cloud computing vendors o er provision of cloud resources on demand whenever they are required by adopters. On-demand self-service resource sourcing is considered a crucial feature of the cloud computing paradigm, as it allows users to scale the required infrastructure up to a substantial level without disrupting the host operations.