HS-SLA: A Hierarchical Self-Healing SLA Model for Cloud Computing

The service level agreement (SLA) is a mutual contract between the service provider and consumer which determines the agreed service level objective (SLO). The common SLA is enforced as a plain documental agreement without any relation to other upper and lower level agreements among different layers of cloud computing. Hence, the cloud computing environment needs the hierarchical and autonomic SLA. This paper proposes the HS-SLA model to enforce the hierarchical self-healing SLA in cloud computing. The self-healing ability includes the SLA monitoring, violation detecting and violation reacting processes. In HS-SLA, the dependent SLAs have a connection to each other hierarchically. This model enables the SLA to check its QoS attributes and notify the current status to dependent SLAs. Additionally, HS-SLA could prevent or propagate the notified violations by an urgent reaction. So, the service providers have a great chance to prevent the violated SLA before sensing by end users. The HS-SLA model is simulated and the experiment results have shown the violation detection and reaction capabilities of the proposed model in a hierarchical cloud environment. Furthermore, in HS-SLA the end users meet the lesser violated SLAs in comparison with the common SLA structure.