Trade-offs in designing web clusters - Internet Computing, IEEE

76 SEPTEMBER • OCTOBER 2002 http://computer.org/internet/ 1089-7801/02/$17.00 ©2002 IEEE IEEE INTERNET COMPUTING H igh-volume Web sites often use clusters of servers to support their architectures. A load balancer in front of such clusters directs requests to the various servers in a way that equalizes, as much as possible, the load placed on each. There are two basic approaches to scaling Web clusters: adding more servers of the same type (scaling out, or horizontally) or upgrading the capacity of the servers in the cluster (scaling up, or vertically).1 Although more detailed and complex models would be required to obtain more accurate results about such systems’ behavior, simple queuing theory provides a reasonable abstraction level to shed some insight on which scaling approach to employ in various scenarios. Typical questions about Web cluster design include