Figure 3-1 shows a typical architecture for delivery of services on the Web.
This server farm uses a three-tier application model, which is normally used for large-scale systems. The three tiers are as follows:
Web servers, which maintain the connections with client browsers and other client devices, parsing and handling input from them, formatting data to be sent to them, serving unchanging (static) web pages, and often being responsible for maintaining transaction context.
Application servers, which run the major transaction and dynamic web page generation systems, ...