This article is an introduction to Apache's document expiration functionality provided by the mod_expires module.
Setting expiration periods for web content enables web browsers to cache content for specific periods of time. As a result, you can reduce the number of HTTP requests that the web server must process, which helps improves web site speed and performance.
The following sample .htaccess configuration demonstrates how to do this:
In this example:
To verify your expiration settings in the .htaccess file are working correctly, you can examine the raw HTTP headers sent between the browser and web server. (To do this, use a browser plugin that displays the raw headers such as Live HTTP headers for Mozilla Firefox, or the Developer Tools feature in Google Chrome.) When content is marked for expiration, Apache adds the following lines to the HTTP response header (the exact values will vary based on your own .htaccess settings):
Cache-Control: max-age=86400 Expires: Thu, 02 Oct 2014 19:02:30 GMT
For more information about the mod_expires module, please visit https://httpd.apache.org/docs/2.2/mod/mod_expires.html.