A Model-Based Framework for SLA Management and Dynamic Reconfiguration

A Service Level Agreement (SLA) is a contract between a service provider and a customer that defines the expected quality of the provided services, the responsibilities of each party, and the penalties in case of violations. In the cloud environment where elasticity is an inherent characteristic, a service provider can cater for workload changes and adapt its service provisioning capacity dynamically. Using this feature one may provide only as many resources as required to satisfy the current workload and SLAs, the system can shrink and expand as the workload changes. In this paper, we introduce a model-based SLA monitoring framework, which aims at avoiding SLA violations from the service provider side while using only the necessary resources. We use UML models to describe all the artifacts in the monitoring framework. The UML models not only increase the level of abstraction but they are also reused from the system design/generation phase. For this purpose, we develop metamodels for SLAs and for monitoring. In the monitoring framework, all abstract SLA models are transformed into an SLA compliance model which is used for checking the compliance to SLAs. To avoid SLA violations as well as resource wasting, dynamic reconfigurations are triggered as appropriate based on the predefined Object Constraint Language (OCL) constraints using thresholds.