Appraches to process dynamic content

Minimal functionality for the Web server is to serve static content, i.e., static files which are pointed to by the URI (Uniform Resource Identifier). Note, that the output produced by the dynamic component is only part of the goal of dynamic content. Dynamic processing may create new files, send mail, search databases, and whatever else any software on the planet can do. Dynamic content can be served in 3 ways:

• Standalone application
   
  
• Integrated application
   
  
• Application server
   
  

Standalone application which is called for each request. Web server passes request parameters to this application, application runs, produces some output, Web server collects the output from it and sends it back to Web browser which originated the request. This is very taxing on the computer, but at the same time easy to set up, and flexible.
 

Integrated application -- it is essantially a subroutine within Web server (or a shared memory object/library module) which is an integral part of Web server. The integrated application has a small overhead, since running it is essentially calling a routine. However, there are time when it may not be an ideal solution. What if you have many different dynamic applications -- your software package becomes fat. Also, if application is computationally intensive -- maybe you want to run requests on different computer(s) than the one which holds Web server. Finally, what if application should be run only behind firewall (you do not want your corporate database to run on the public Web server).
 

Application server -- an application which processes specific type of requests and runs perpetually as a daemon/service. It accepts requests from Web server via some communication protocol, and returns results back to the Web server. It is always up, and does not need to be started for each request. It can run on another computer, and finally, there maybe many application servers running in parallel, and the load can be spread between them evenly (how do you think Search Engines run?).