SLA and Profit-aware SaaS Provisioning through Proactive Renegotiation

Software-as-a-Service (SaaS) providers offer on-demand, highly scalable applications to the end users. To maximize their profit, the providers must make profit-aware scheduling decisions about assigning client requests to virtual resources, while respecting the agreed upon Service-Level Agreement (SLA). Given the highly dynamic nature of the cloud environment, unexpected events may affect the initial scheduling plans, which leads to unanticipated SLA violations. Thus, an unaccounted event may create a lose-lose situation between provider and client. If the SLA is violated the provider must pay the potentially high penalty that is negotiated within the original SLA. But from the client's viewpoint, an SLA violation may cause cancellation of a business-critical job, and no ordinary SLA penalty can compensate for the loss of the client's business. The provider's reputation could also suffers as the number of such SLA violations grows, resulting in loss of future clients. On the contrary of most existing work that assume that once established the SLA cannot be modified, we propose to convert the lose-lose situation into a win-win one through an automated renegotiation mechanism. When an event threatens a lose-lose violation of the SLA, the renegotiation mechanism is launched to establish a new SLA that limits the losses on the two sides. Experiments show that this new approach minimizes the loss in profit of the provider and minimizes the number of cancelled jobs experienced by the client, as compared with enforcing the original SLA.