Different steps for measuring performance of distributed web server system are shown in Figure 4.1. Load generator (any third party benchmark program) runs on nodes at client side and generates HTTP requests to distributed web server system. Distributed web server system is part of test bed and its components are modified corresponding to load balancing strategy used in web server system. Additional software components running at these nodes collect statistical information, which is collected and processed. After processing this statistical data, performance is analyzed and results are presented.
Web server system in test bed uses the same general hierarchical structure shown in Figure 3.1. This model allows one to emulate behavior of multiple networks in different geographical regions. Single server can be used instead of one cluster containing front node and multiple servers, so this test bed allows us to emulate cluster based as well as independent server based architectures or web server systems containing mixture of both.
Web server system consists of many clusters distributed geographically all over the world placed at strategic locations in possibly different time zones. Similarly client domains modeled by multiple client processes on one or more clients also are divided in different geographical regions. Thus it enables us to take into account variation of different parameters like delay, loss, request rate etc. from each geographical region.
Since we have tried to emulate real Internet like system and used standard components and protocols, we expect to use same test bed for measuring performance of almost every load balancing web server system with minimal modification in some components corresponding to mechanism used in the system. Below we briefly describe software components that run on different components of test bed
