The Common Gateway Interface, normally referred to as
The Common Gateway Interface, normally referred to as CGI, was one of the first practical techniques for creating dynamic content. With CGI, a web server passes certain requests to an external program. The output of this program is then sent to the client in place of a static file. The advent of CGI made it possible to implement all sorts of new functionality in web pages, and CGI quickly became a de facto standard, implemented on dozens of web servers. It’s interesting to note that the ability of CGI programs to create dynamic web pages is a side effect of its intended purpose: to define a standard method for an information server to talk with external applications. This origin explains why CGI has perhaps the worst life cycle imaginable. When a server receives a request that accesses a CGI program, it must create a new process to run the CGI program and then pass to it, via environment variables and standard input, every bit of information that might be necessary to generate a response. Creating a process for every such request requires time and significant server resources, which limits the number of requests a server can handle concurrently. Figure 1-1 shows the CGI life cycle. Figure 1-1. The CGI life cycle Even though a CGI program can be written in almost any language, the Perl programming language has become the predominant choice. Its advanced textprocessing capabilities are a big help in managing the details of the CGI interface. Writing a CGI script in Perl gives it a semblance of platform independence, but it also requires that each request start a separate Perl interpreter, which takes even more time and requires extra resources. Another often-overlooked problem with CGI is that a CGI program cannot interact with the web server or take advantage of the server’s abilities once it begins execution because it is running in a separate process. For example, a CGI script cannot write to the server’s log file. For more information on CGI programming, see CGI Programming on the World Wide Web by Shishir Gundavaram (O’Reilly). FastCGI A company named Open Market developed an alternative to standard CGI named FastCGI. In many ways, FastCGI works just like CGI the important difference is that FastCGI creates a single persistent process for each FastCGI program, as shown in Figure 1-2. This eliminates the need to create a new process for each request.
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