Role of System Modeling for Audit of QoS Provisioning in Cloud Services

Given cloud-based realization of a distributed system S, QoS auditing enables risk analysis and accounting of SLA violations under various security threats and resource depletion faced by S. The problem of QoS failures and security infringements arises due to third-party control of the underlying cloud resources and components. Here, a major issue is to reason about how well the system internal mechanisms are engineered to offer a required level of service to the application. We employ computational models of S to determine the optimal feasible output trajectory and verify how close is the actual behavior of S to this trajectory. The less-than-100% trust between the various sub-systems of S necessitates our model-based analysis of the service behavior vis-a-vis the SLA negotiated with S. The paper describes the modeling techniques to analyze the dependability of such a cloud-based system.