How to configure mod_expires headers to manage cache?

What is mod_expires?

An Apache module called mod_expires provides guidance to web browsers on how to handle cache management. Web browsers are informed about how long to save pictures, HTML files, and other files by the mod_expires settings. If this setting is made, subsequent requests from the same user will see faster page loads.

The max-age directive of the Cache-Control HTTP header and the settings of the HTTP header “Expires” in server replies are controlled by the mod_expires module. Either the client’s access time or the last modification date of the source file may be used to determine the expiration date.

Apache mod_expires page

Use the following code to verify if the expires module is loaded:

httpd -M | grep expires

#[root@web /]# httpd -M | grep expires
expires_module (static)
[root@web /]#

 Configuring mod_expires rules

You can configure mod_expires rules in the .htaccess file from the root directory of your site.

Example:

<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access plus 1 year"
ExpiresByType image/jpeg "access plus 1 year"
ExpiresByType image/gif "access plus 1 year"
ExpiresByType image/png "access plus 1 year"
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/pdf "access plus 1 month"
ExpiresByType text/x-javascript "access plus 1 month"
ExpiresByType application/javascript "access plus 1 month"
ExpiresByType image/x-icon "access plus 1 year"

#default expiry time
ExpiresDefault "access plus 2 days"
</IfModule>

You can add or remove MIME types as per your needs. You can use the above as a template.

The objective is to specify which MIME types should be cached. Begin each line with ExpiresByType, then MIME type followed by time period.

Testing if mod_expires works

Use the curl command to access a file from the site if you have SSH access.

curl -is https://example.com/file

For accessing a png file, here is an example:

[root@web /]# curl -is https://demo.hostvento.com/logo.png
HTTP/2 200
date: Tue 9 November 2021 14:40:22 GMT
server: Apache/2
last-modified: Fri, 10 February 2018 23:58:37 GMT
etag: "244c-4d58fcdd26540"
accept-ranges: bytes
content-length: 9292
cache-control: max-age=31536000
expires: Wed, 9 November 2022 14:40:22 GMT
content-type: image/png

[root@web /]#

The above example explains that the server is instructing the client to cache the file for one year i.e. from the present date till 9 November 2022.

That is how you can manage the cache on your web browser using Apache module mod_expires.