Analysis of Response Time Percentile Service Level Agreements in SOA-Based Applications

A large number of enterprise, web-based, distributed software applications are designed on Service Oriented Architecture (SOA) principles and hosted in large scale datacenters managed by cloud providers. Typically, Service Level Agreements (SLAs) are negotiated between the consumers of the cloud platform services and the cloud provider. In this work, we consider SLAs that involve percentiles of response times as part of the performance metrics; the SLAs stipulate that a penalty be charged to the cloud provider if the SLA targets are not met. The main motivation for considering such SLAs is their potential for price differentiation. We focus our analysis on the effects the penalty function has on the achieved response time percentiles. In particular, we analyze the effect of three commonly deployed choices (linear, exponential or step-wise functions) to relate the penalty charged and the achieved percentile. This analysis is NP-hard, so we employ a heuristic algorithm that is based on simulated annealing. Our results indicate that the linear penalty charging function is "best\´\´ in the sense that it maximizes the achieved response time percentiles.