Proxy means to act on behalf of another. In the context of a web server, this means one server fetching content from another server, then returning it to the client. For example, you may have several web servers that hide behind a proxy server. The proxy server is responsible for having requests end up going to the right backend server.
mod_proxy, which comes with Apache, handles proxying behavior. The recipes in this chapter cover various techniques that can be used to take advantage of this capability. We discuss securing your proxy server, caching content proxied through your server, and ways to use mod_proxy to map requests to services running on alternate ports.
Additional information about mod_proxy can be found at http://httpd.apache.org/docs/mod/mod_proxy.html for Apache 1.3, or http://httpd.apache.org/docs-2.0/mod/mod_proxy.html for Apache 2.0.
Please make sure you don't enable proxying until you understand the security concerns involved and have taken steps to secure your proxy server. (See Recipe 6.20 for details.)
You may also wish to consider a dedicated proxy server, such as Squid (http://www.squid-cache.org/), which is focused entirely on one task, and thus has more options related to this task.