Service Level Aware - Contract Management

The success achieved by Cloud Computing Services (CCSs) in modern IT scenarios is nowadays a matter of fact and service offerings between providers and customers continuously grow up and widen their scope. Similarly, service offerings are more and more based upon dynamic reservation and allocation of network, storage and computational resources, the hiding of visibility of internal IT components, as well as the pay-per-use paradigm. The main drawback of such a situation is represented by the complexity in composing services to satisfy users´ requests, as well as in performance monitoring and service level comparisons. Effective strategies are then needed to model IT service contracts and corresponding Service Level Agreements (SLAs), as well as their composition. However, the lack of expressivity in current SLA specifications and the inadequacy of tools for managing SLA and contract compositions is relevant. Therefore, we present a possible extension of WSLA, a widely known SLA description language, for modeling contracts and SLAs suitable to support contract owners during service composition and monitoring phases. An ad-hoc developed tool based on the usage of directed tree-graphs and of a rule-based engine is examined to assess the feasibility of the proposed model and to simplify SLA and contract composition.