Tutorials > How to optimize Apache static file caching on Ubuntu 18.04

How to optimize Apache static file caching on Ubuntu 18.04

Published on: 16 January 2020

Apache Cache

This guide shows how to correctly configure the header expiration settings with Apache, optimizing the performance of the web server in serving static files, such as images, CSS or JavaScript files.

A lot of bandwidth on your server will be saved, by setting a minimum date for caching file. As a result, by using the client browser cache, hosted websites will load faster.

First, connect to your server via an SSH connection. If you haven’t done so yet, following our guide is recommended to connect securely with SSH. In case of a local server, go to the next step and open the terminal of your server.

Enabling the necessary modules

To enable the sending of the necessary Headers, first enable the related Apache module:

$ sudo a2enmod expires

And then restart the service:

$ sudo service apache2 restart 

Module configuration

The module configuration can be inserted in the following :

  • In Apache configuration: it will be inherited by all the sites controlled by Apache (virtual and non-virtual hosts)

  • In a virtual host container

  • Within the <Directory> directive or .htaccess file

In the following example, it is inserted in the default site configuration:

$ sudo vim /etc/apache2/sites-available/000-default.conf

Then add the following configuration:

<IfModule mod_expires.c>

          <FilesMatch "\.(jpe?g|png|gif|js|css)$">

                      ExpiresActive On

                      ExpiresDefault "access plus 1 week"



Through the FilesMatch directive which files should be kept by the client browser (in this case css, jpg, png, gif and js) are being specified.hile, through ExpiresDefault, how long they should be kept (in this example, a week) for is being indicated.

To apply the changes, restart Apache:

$ sudo service apache2 restart 

In addition to FilesMatch and ExpiresDefault method, ExpiresByType can be used to set the Header Expires for every type of file, for example:

<IfModule mod_expires.c>

 ExpiresActive on
 ExpiresByType image/jpg "access plus 60 days"
 ExpiresByType image/png "access plus 60 days"
 ExpiresByType image/gif "access plus 60 days"
 ExpiresByType image/jpeg "access plus 60 days"
 ExpiresByType text/css "access plus 1 days"
 ExpiresByType image/x-icon "access plus 1 month"
 ExpiresByType application/pdf "access plus 1 month"
 ExpiresByType text/javascript "access plus 1 week"


By using this method, a more granular control over the duration of the cache can be obtained and the caching of Ajax data, by not inserting the mime-type application/javascript can be obtained.

For both directives, the syntax for indicating the duration of the cache is the same, that is to say:

“[base] plus [valore] [tipo] [valore] [tipo] [valore] [tipo] …”

The base value can be:

  • access: client request date

  • modification: modification date of the file

While the type can have the following values:

  • years: years

  • months: months

  • weeks: weeks

  • days: days

  • hours: hours

  • minutes: minutes

  • seconds: seconds

Some examples of configuration are:

# One year cache expiry 
ExpiresByType image/jpeg "access plus 1 year"

#Furthermore, more than one unit of measurement in sequence can be added. For example:

# Set 1-month, 15- day and 2-hour expiry
ExpiresByType text/html "access plus 1 month 15 days 2 hours"

# Cache expiry from the file modification date more than 5 hours and 3 minutes 
ExpiresByType image/gif "modification plus 5 hours 3 minutes"

Please, remember that if you have to change the content of a cached file, the latter will not be downloaded by the clients until the caching time expires. This could cause malfunctions on your websites.

Although clients cannot be forced to ignore the previously saved cache, several techniques can be used to avoid this problem. 

A method often used is to rename the just modified file (for example from style.css to style-v2.css) or change the links by adding a version number, for example from:

<script src="https://www.domain.com/js/myScript1.js"></script>

to the following:

<script src="https://www.domain.com/js/myScript1.js?v=3.1"></script>