SSI (Server Side Includes)

There are some problems with CGI of course. Perhaps the most serious problem is speed. Every time the web server gets a CGI request, it needs to execute the CGI application.

What's worse, if you are using a web server into which the Perl interpreter has not already been embedded, you will need to load the Perl interpreter every time. If you begin to get thousands of requests per second, this could quickly cause your web services to grind to a halt.

One way to get around this problem is to embed the processing into the web server itself. Rather than rely on another layer, most web servers provide several ways to extend the web server itself; to add logic and processing power.

The earliest technology to take advantage of this idea was SSI (Server Side Includes). The concept of SSI is simple. An application developer codes special tags into her HTML document. Those special tags are understood by the web server and can be translated on the fly by the web server as the HTML document passes through on its way to the browser.

WARNING: NCSA notes that having the server parse documents is "a double edged sword. It can be costly for heavily loaded servers to perform parsing of files while sending them. Further, it can be considered a security risk to have average users executing commands as the server's User."

Perl is the Right Tool for the Job
Introduction to the Web Application Development Environment (Tools)
SSI Directives