A Formal Approach for Service Composition in a Cloud Resources Sharing Context

Composition of Cloud services is necessary when a single component is unable to satisfy all the user's requirements. It is a complex task for Cloud managers which involves several operations such as discovery, compatibility checking, selection, and deployment. Similarly to a non Cloud environment, the service composition raises the need for design-time approaches to check the correct interaction between the different components of a composite service. However, for Cloud-based service composition, new specific constraints, such as resources management, elasticity and multitenancy have to be considered. In this work, we use Symbolic Observation Graphs (SOG) in order to abstract Cloud services and to check the correction of their composition with respect to event-and state-based LTL formulae. The violation of such formulae can come either from the stakeholders' interaction or from the shared Cloud resources perspectives. In the former case, the involved services are considered as incompatible while, in the latter case, the problem can be solved by deploying additional resources. The approach we propose in this paper allows then to check whether the resource provider service is able, at run time, to satisfy the users' requests in terms of Cloud resources.