Setting of CacheControl headers on apache

Cache Control with mod_expires and mod_headers

For Apache, mod_expires and mod_headers handle cache control through HTTP headers sent from the server. Since they are not installed by default, have your server administrator install them for you. For Apache/1.3x, enable the expires and headers modules by adding the following lines to your httpd.conf configuration file.

LoadModule expires_module libexec/mod_expires.so
LoadModule headers_module libexec/mod_headers.so

AddModule mod_expires.c
AddModule mod_headers.c
...
AddModule mod_gzip.c

Note that the load order is important in Apache/1.3x, mod_gzip must load last, after all other modules.

For Apache/2.0, enable the modules in your httpd.conf file like this.

LoadModule expires_module modules/mod_expires.so
LoadModule headers_module modules/mod_headers.so
LoadModule deflate_module modules/mod_deflate.so

mod_deflate is the native compression module in Apache/2.0 (although mod_gzip does a better job of handling wayward browsers). In this case, the load order does not matter, as Apache/2.0 handles this for you.
Target Files by Extension for Caching

One quick way to enable cache control headers for existing sites is to target files by extension. Although this method has some disadvantages (notably the requirement of file extensions), it has the virtue of simplicity. To turn on mod_expires set ExpiresActive to on.

ExpiresActive On

Next target your website's root HTML directory to enable caching for your site in one fell swoop.

<Directory "/home/website/public_html">
Options FollowSymLinks MultiViews
AllowOverride All
Order allow,deny
Allow from all
ExpiresDefault A300
<FilesMatch "\.html$">
Expires A86400
</FilesMatch>
<FilesMatch "\.(gif|jpg|png|js|css)$">
Expires A2592000
</FilesMatch>
</Directory>

ExpiresDefault A300 sets the default expiry time to 300 seconds after access (A). Using M300 would set the expiry time to 300 seconds after file modification. The FilesMatch segment sets the cache-control header for all .html files to 86400 seconds (1 day). The second FilesMatch section sets the cache-control header for all images, external JavaScripts and CSS files to 2592000 seconds (30 days).

Note that you can target your files with more granularity using multiple directory sections, like this:

<Directory "/home/website/public_html/images/logos/">

For truly dynamic content you can force resources to not be cached by setting an age of zero seconds and to not store the resource anywhere.

<Directory "/home/website/cgi-bin/">
Header Set Cache-Control "max-age=0, no-store"
</Directory>

Target Files by MIME Type

The disadvantage of the above method is the reliance on the existence of file extensions. In some cases webmasters elect to use extensionless URLs for portability and performance (see Rewrite URLs with Content Negotiation). A better method is to use the ExpiresByType command of the mod_expires module. As the name implies, ExpiresByType targets resources for caching by MIME type, like this.

ExpiresActive On
ExpiresDefault "access plus 300 seconds"

<Directory "/home/website/public_html">
Options FollowSymLinks MultiViews
AllowOverride All
Order allow,deny
Allow from all
ExpiresByType text/html "access plus 1 day"
ExpiresByType text/css "access plus 1 day"
ExpiresByType text/javascript "access plus 1 day"
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/jpg "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType application/x-shockwave-flash "access plus 1 day"
</Directory>



<FilesMatch "\.(ico|pdf|flv|jpg|jpeg|png|gif|js|css|swf)$">
Header set Expires "Mon, 22 Dec 2019 10:00:00 GMT"
</FilesMatch>