Dependability Modeling and Certification of Cloud-Based Distributed Systems

A system that is highly dependable under hostile conditions but whose dependability cannot be easily evaluated prior to the deployment of applications is less desirable than a system with lower but predictable dependability. This is because a decision-making on the deployment of high assurance systems is often based on a risk analysis of application failures. For system services implemented on a cloud, the problem of system certification assumes added importance because of third-party control of cloud resources and the attendant problems of faults, QoS degradations, and security violations. Our paper treats system dependability as an application-level QoS for management purposes, and advocates a probabilistic evaluation of dependability. Our approach is corroborated by measurements on system-level prototypes and simulation analysis of system models in the face of hostile environment conditions. A case study of content-distribution networks anchored on cloud infrastructures is also described.