An Adaptive Trust-aware Brokerage Model for Cross-cloud Federation

Abstract

Establishing trust in cloud computing has been a major concern for cloud users since the very beginning of pay-as-you-go service. In the recent years, cross-cloud federation has enabled cloud providers to share or lease resources from each other. Contrary to the hesitation of cloud users for cloud adoption, it is now the cloud providers that are reluctant to take part in federation due to lack of trust on their unknown counterparts. A recent void has been observed to address the challenges of trustworthy resource exchanges within the federation. This research has established that trust awareness among cloud providers requires a comprehensive trust framework that is aligned with the nature of federation.

A detailed requirement analysis for trust in cross-cloud federation has been performed in this research. This analysis is based on four founding principles of cloud-to-cloud trust paradigm namely bi-directionality, composite trust, delegation control and resource aware trust evaluation. Afterwards, requirements originated from these principles are aligned with the attributes of trust and cloud federation with the help of a detailed requirement matrix. Keeping in view this requirement matrix, an adaptive trust-aware brokerage model has been developed. This model offers dynamic trust establishment approaches that are a function of relationship among service providers. Three different approaches i.e. Conjunctive Accumulation of Trust (ConAccT), Numerical Accumulation of Trust (NAccT) and Cooperation Threshold Estimation (CTE) are developed as part of the proposed model. ConAccT is based on belief calculus and may be useful in case of highly competitive collaborating scenarios where detailed analysis of trust is required to decide cooperation among Cloud Service Providers (CSPs). NAccT approach is based on numerical calculus and is useful in less competitive scenarios and can be combined with metrics other than trust i.e. performance, availability, resource specifications etc. CTE approach is an extension to NAccT and presents a use case of utilizing the performance metric of a CSP combined with its trust metric to evaluate risk of failure in a collaborative project. The significance of these approaches has been verified by implementing the adaptive trust-aware model as a trusted broker based Clouds4Coordination (C4C) system developed for Architecture/Engineering/Construction (AEC) industry. This C4C system is currently implemented in United Kingdom in collaboration with Cardiff University, UK and Rutgers Discovery Informatics Institute (RDI2), USA. Experimental evaluation of these approaches suggests their suitability in varying scenarios of collaborative computing in construction industry. It has been verified that trust-aware relationships within the federation stays for a longer duration of time during collaborative projects. Moreover, an in depth analysis of proposed approach has shown that trust awareness is beneficial in terms of successful service delivery, earlier project completion and reduction in uncertainty of collaboration. A comparative analysis with state-of-art approaches have demonstrated the efficiency of proposed approaches to identify participants of federation that can cause potential risks and unnecessary delays in the projects.