There are three typical choices for an Oracle Application Express installation web servers : Oracle HTTP server with mod_plsql, Embedded PL/SQL Gateway (EPG) and the Oracle APEX Listener. Choosing one of these servers relates not only to features and performance, but also to the preferred technology stack. As EPG is an easy to configure lightweight server; it is not suited for enterprise applications or web application with heavy traffic. Oracle HTTP server might be the most common choice, but the APEX Listener is a Java 2EE alternative that might fit better into a Java technology stack.
Oracle HTTP server with mod_plsql
The Oracle HTTP server uses the mod_plsql extension to communicate with the Oracle database and with APEX. The server is delivered as a component of Oracle Fusion Middleware and is designed to serve both static and non-static web pages, acting as a HTTP listener for the Oracle Weblogic Server.
The Oracle HTTP Server is, in fact, an implementation of Apache HTTP server. Mod_plsql, as an extension, will provide HTTP generation from PL/SQL code, by mapping browser requests to database stored procedures.
A complete web request flow using this configuration is as follows: