Abstract

Fueled by the growing acceptance of the Web Services Architecture, an emerging trend in application service delivery is to move away from tightly coupled systems towards structures of loosely coupled, dynamically bound systems to support both long and short business relationships. It appears highly likely that the next generation of e-Business systems will consist of an interconnection of services, each provided by a possibly different service provider, that are put together on an ``on demand'' basis to offer an end to end service to a customer.

Such an environment, which we call Dynamic e-Business (DeB), will be administered and managed according to dynamically negotiated Service Level Agreements (SLA) between service providers and customers. Consequently, system administration will increasingly become SLA-driven and needs to address challenges such as dynamically determining whether enough spare capacity is available to accommodate additional SLAs, the negotiation of SLA terms and conditions, the continuous monitoring of a multitude of agreed-upon SLA parameters and the troubleshooting of systems, based on their importance for achieving business objectives.

A key prerequisite for meeting these goals is to understand the relationship between the cost of the systems an administrator is responsible for and the revenue they are able to generate, i.e., a model needs to be in place to express system resources in financial terms. Today, this is usually not the case.

In order to address some of these problems, this paper presents the Web Service Level Agreement (WSLA) framework for defining and monitoring SLAs in inter-domain environments. The framework consists of a flexible and extensible language based on the XML schema and a runtime architecture based on 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 tie them to managed resource instrumentations. A Java-based implementation of this framework, termed SLA Compliance Monitor, is publicly available as part of the IBM Web Services Toolkit.

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