A cluster is one of those industry concepts that everyone sort of understands but for which no universally applicable definition exists. Generally speaking, a cluster is a group of two or more servers that share responsibility for a set of tasks and resources for carrying out those tasks. That definition is probably vague enough to avoid being flagrantly wrong in any of the half-dozen vendor-specific contexts in which it might be used. However, nonspecificity is a luxury of the marketing department and has no place in IT.
In the context of BEA WebLogic server, a cluster consists of three elements:
|HTTP Server||This may be either the HttpClusterServlet provided with WebLogic, or some third-party web server configured with a proxy plug-in. ...|