Monitoring the QoS of Web Services using SLAs - Computing metrics for composed services
Chrysostomos Zeginis · 2009
The Web services are an emerging technology which attracts a lot of attention from both academic and industry areas these recent years. Once Web services become operational, their execution needs to be managed and monitored to gain a clear view of how services perform within their operational environment, make management decisions and perform control actions to modify and adjust their behavior. Many approaches have been proposed and have proven that Web services’ monitoring is very crucial for successful invocations. This thesis analyzes the methods that can be used to monitor the execution of a Web service, in order to comply with the corresponding Service Level Agreement (SLAs) and the ways various metrics can be computed for composed services, having available the metric values of the constituent Web services. Nowadays, most of Web service providers sign SLA contracts with their clients to guarantee the offered functionality of their services. A monitoring system is introduced to check violations in the pre-agreed metric values of SLAs. These results can be very helpful for service providers, who can then take corrective actions to improve their services. As far as the computation of QoS for composed Web services is concerned, this thesis proposes some basic metric types, provided that we know the composition pattern. Based on this pattern, appropriate formulas are used to compute the response time, the throughput, the reliability and the cost of the composed Web services. The validity of these formulas is verified with experimental results.