Consider an online auction site that has a large number of registered customers. The overall architecture of the site is shown in Fig. 8.1. Users access the site from the Internet after passing through the necessary firewall. The site itself consists of three servers: a Web server, an application server, and a database server. The Web server manages all the Web pages and handles all the direct interactions with the customers. The application server implements the core business logic of the site. The database server is used to store persistent data about auctions, bids, and registered customers. Each of these servers has one CPU and one disk. The generalization to the case of additional servers, servers with more than one CPU, and servers with multiple disks is straightforward and is discussed later in the chapter.
Figure 8.1. Online auction site architecture.
The online auction site offers the following services to its customers: create and broker auctions, search for auctions based on categories of items and keywords, monitor existing bids on open auctions, and place bids at strategic times on open auctions. In order to create an auction or to place a bid, customers are required to login to the site.