The WSLA Framework: Specifying and Monitoring Service Level Agreements for Web Services

We describe a novel framework for specifying and monitoring Service Level Agreements (SLA) for Web Services. SLA monitoring and enforcement becomes increasingly important in a Web Service environment where enterprises rely on services that may be subscribed dynamically and on demand. For economic and practical reasons, we want an automated provisioning process for both the service itself as well as the SLA management system. It measures and monitors the QoS parameters, checks the agreed-upon service levels, and reports violations to the authorized parties involved in the SLA management process. The Web Service Level Agreement (WSLA) framework, our approach to these issues, is targeted at defining and monitoring SLAs for Web Services. Although WSLA has been designed for a Web Services environment, it is applicable as well to any inter-domain management scenario such as business process and service management or the management of networks, systems and applications in general. The WSLA framework consists of a flexible and extensible language based on XML Schema and a runtime architecture comprising several SLA monitoring services, which may be outsourced to third parties to ensure a maximum of accuracy. WSLA enables service customers and providers to unambiguously define a wide variety of SLAs, specify the SLA parameters and the way how they are measured, and relate them to managed resource instrumentations. Upon receipt of an SLA specification, the WSLA monitoring services
are automatically configured to enforce the SLA. An implementation of the WSLA framework, the
SLA Compliance Monitor, is publicly available as part of the IBM Web Services Toolkit.