SLA Monitor: A System for Dynamic Monitoring of Adaptive Web Services

Service Level Agreements (SLAs) need to be monitored at runtime to assure that the Business Level Agreements (BLAs) / Business Level Objectives (BLOs) are indeed satisfied in the realized business workflow and allow the organization to adjust its business processes best to the environment. In this paper, we show how multiple SLAs specified on various observable attributes can be formally specified, automatically synthesized and plugged into the underlying workflow service engine to assure such a conformance. Such a conformance validation allows the workflow engine to ensure the satisfaction of BLA/BLO and adapt as per requirements. Note that most of the SLAs, can be characterized formally either as safety properties based on bounded history of the business events/attributes or some standard quantification of the performance attributes. In our work, the former is specified using a temporal logic called SL that has been shown to have the expressive power of regular safety properties, we confine to a fragment of SL called DSL, for which the accepting automata is deterministic. The latter is specified using standard system/user provided macros based on the observable QoS attributes. In the paper, we first describe an automatic synthesis (model checking) of monitors from the DSL formulae realized through a model checking algorithm, and then provide an overview of the integrated environment called SLA Monitor for specifying and monitoring conformance. The effectiveness of specifying SLAs in DSL is demonstrated through examples and SLA Management is illustrated.