HTTP: The Definitive Guide

Setting Cache Controls

Different web servers provide different mechanisms for setting HTTP cache-control and expiration headers. In this section, we’ll talk briefly about how the popular Apache web server supports cache controls. Refer to your web server documentation for specific details.

Controlling HTTP Headers with Apache

The Apache web server provides several mechanisms for setting HTTP cache-controlling headers. Many of these mechanisms are not enabled by default—you have to enable them (in some cases first obtaining Apache extension modules). Here is a brief description of some of the Apache features:

mod_headers

The mod_headers module lets you set individual headers. Once this module is loaded, you can augment the Apache configuration files with directives to set individual HTTP headers. You also can use these settings in combination with Apache’s regular expressions and filters to associate headers with individual content. Here is an example of a configuration that could mark all HTML files in a directory as uncachable:

<Files *.html>
  Header set Cache-control no-cache
</Files>

mod_expires

The mod_expires module provides program logic to automatically generate Expires headers with the correct expiration dates. This module allows you to set expiration dates for some time period after a document was last accessed or after its last-modified date. The module also lets you assign different expiration dates to different file types and use convenient verbose descriptions, like “access ...