Administering an ISP Installation

Calculating Hardware Needs

To set up an installation for a Web-based retail business, you need to determine how many Web servers are actually needed to host a certain application. You can start with one server, test it, and then upgrade it as necessary.

After testing the single server, you might find that the processor utilization is extremely high, that the cache-hit rates are low, and that the server has many requests lined up in the queue. At this point, you can solve the problem by adding processors, memory, and other hardware devices to increase performance. If these solutions fail to improve performance, you can add Web servers.

While there is no mathematical formula for determining the optimum number of servers you should add, you can select from a variety of Web stress tools to help you decide. One such tool is the Web Application Stress Tool. This tool allows you to simulate the load of thousands of users on your site. In conjunction with the System Monitor, you can easily determine at what point a single Web server will crash. A major bottleneck for any Web server is at the HTTP layer. To combat that bottleneck, you should add Web servers, with the ultimate goal of building a Web cluster.

After stressing the single server, you might decide to upgrade so that you can handle a customer’s Web site more efficiently. For example, you can add two more Web servers to make up the first tier of your Web cluster.