In the previous recipes in this chapter, our Apache service only served static content, which means that everything requested by a web-browser already existed in a constant state on the server, for example as plain HTML text files that don't change. Apache simply sends the content of a specific file from the web server to the browser as a response where it then gets interpreted and rendered. If there were no way to change the contents sent to the client, the Internet would be really boring and not the huge success it is today. Not even the simplest example of dynamic content, such as showing a web page with the web server's current local time would be possible.
Therefore, early in the 1990's, some smart people started inventing mechanisms to make communication possible between a web server and some executable programs installed on the server to generate web pages dynamically. This means that the content of the HTML sent to the user can change in response...