Control Browser Caching

How To Control Browser Caching with Apache 2

HTTP headers are transparent to the end user and most people don't even care that they exist at all. Despite this, they are included at the beginning of every response that comes from your server and they contain important information about that response. The most common information includes the date, type of server sending the HTTP response, and encoding of the HTTP response.

You need both the mod_expires and mod_headers modules compiled and loaded into your Apache 2 installation.

You can check this by,

apachectl -M | grep expires

...should return:

expires_module (shared)

apachectl -M | grep headers

… should return:

headers_module (shared)

Here is a code snippet of an Apache 2 directive that we will be using. This directive can be modified to suite your tastes or it can just be used "as is" for most users. The directives here can be placed into the <Directory> directive of your virtual host in http.conf or it can be placed loosely in a .htaccess file in the root of your website.

<IfModule mod_expires.c>

  ExpiresActive On

  ExpiresDefault "access plus 1 seconds"

  ExpiresByType text/html "access plus 1 seconds"

  ExpiresByType image/gif "access plus 120 minutes"

  ExpiresByType image/jpeg "access plus 120 minutes"

  ExpiresByType image/png "access plus 120 minutes"

  ExpiresByType text/css "access plus 60 minutes"

  ExpiresByType text/javascript "access plus 60 minutes"

  ExpiresByType application/x-javascript "access plus 60 minutes"

  ExpiresByType text/xml "access plus 60 minutes"

</IfModule>

This code can be placed in the .htaccess files for specific directories, or in your root web directory.

If you are adding the above code in the Apache httpd.conf file, you need to restart the service in order to the caching get reflected.

systemctl restart httpd

If you are interested, full documentation of the expires directive can be found on Apache's website along with different syntax formats than the ones used here.

About Mod_expires & Mod_headers

Mod_expires

http://httpd.apache.org/docs/2.2/mod/mod_expires.html

This module controls the setting of the Expires HTTP header and the max-age directive of the Cache-Control HTTP header in server responses. The expiration date can set to be relative to either the time the source file was last modified, or to the time of the client access.

These HTTP headers are an instruction to the client about the document's validity and persistence. If cached, the document may be fetched from the cache rather than from the source until this time has passed. After that, the cache copy is considered "expired" and invalid, and a new copy must be obtained from the source.

# BEGIN Expires

<ifModule mod_expires.c>

ExpiresActive On

ExpiresDefault "access plus 1 seconds"

ExpiresByType text/html "access plus 1 seconds"

ExpiresByType image/gif "access plus 2592000 seconds"

ExpiresByType image/jpeg "access plus 2592000 seconds"

ExpiresByType image/png "access plus 2592000 seconds"

ExpiresByType text/css "access plus 604800 seconds"

ExpiresByType text/javascript "access plus 216000 seconds"

ExpiresByType application/x-javascript "access plus 216000 seconds"

</ifModule>

# END Expires

Mod_headers

http://httpd.apache.org/docs/2.2/mod/mod_headers.html

This module provides directives to control and modify HTTP request and response headers. Headers can be merged, replaced or removed.

# BEGIN Caching

<ifModule mod_headers.c>

<filesMatch "\.(ico|pdf|flv|jpg|jpeg|png|gif|swf)$">

Header set Cache-Control "max-age=2592000, public"

</filesMatch>

<filesMatch "\.(css)$">

Header set Cache-Control "max-age=604800, public"

</filesMatch>

<filesMatch "\.(js)$">

Header set Cache-Control "max-age=216000, private"

</filesMatch>

<filesMatch "\.(xml|txt)$">

Header set Cache-Control "max-age=216000, public, must-revalidate"

</filesMatch>

<filesMatch "\.(html|htm|php)$">

Header set Cache-Control "max-age=1, private, must-revalidate"

</filesMatch>

</ifModule>

# END Caching