Until now wWe have largely danced around the issue of Web clusters. Most of the solutions so far in this book have worked under the implicit assumption that we were running a single Web server for the content. Many of those coding methods and techniques work perfectly well as you scale past one machine. A few techniques were designed with clusters in mind, but the issues of how and why to build a Web cluster were largely ignored. In this chapter we’ll address these issues.
A group of machines all serving an identical purpose is called a cluster. Similarly, an application or a service is clustered if any component of the application or service is served by more than one server.