Imagine a scenario where you start your business as a small service providing a web site. After a while your business becomes very popular, and at some point you realize that it has outgrown the capacity of your machine. Therefore, you decide to upgrade your current machine with lots of memory, a cutting-edge, super-expensive CPU, and an ultra-fast hard disk. As a result, the load goes back to normal—but not for long. Demand for your services keeps on growing, and just a short time after you've upgraded your machine, once again it cannot cope with the load. Should you buy an even more powerful and very expensive machine, or start looking for another solution? Let's explore the possible solutions for this problem.
A typical web service consists of two main software components: the database server and the web server.
A typical user-server interaction consists of accepting the query parameters entered into an HTML form and submitted to the web server by a user, converting these parameters into a database query, sending it to the database server, accepting the results of the executed query, formatting them into a nice HTML page, and sending it to a user's Internet browser or another application that created the request (e.g., a mobile phone with WAP browsing capabilities). This process is depicted in Figure 12-9.
This schema is known as a three-tier architecture in the computing world. In a three-tier architecture, you split up several processes of your computing solution between different machines:
We are interested only in the second and the third tiers; we don't specify user machine requirements, since mod_perl is all about server-side programming. The only thing the client should be able to do is to render the generated HTML from the response, which any simple browser will do.