How to Specify a Vary: Accept-Encoding Header in Apache

Adding the Vary: Accept-Encoding header in Apache ensures that the server informs caching systems (browsers, CDNs, proxies) to store and serve different versions of a resource based on whether compression is used.

For the modules and the broader Apache cache/headers setup, see How to Install and Enable mod_headers in Apache, How to Enable and Configure mod_headers in Apache, Understanding mod_headers in Apache, and How to Enable and Configure mod_expires in Apache for Caching.

Here is how to modify Apache to specify the Vary: Accept-Encoding header.

Ensure the following Apache modules are enabled:

1. mod_headers: To modify HTTP headers.
2. mod_deflate: To enable gzip compression (optional but recommended).

Run the following commands to enable these modules:

sudo a2enmod headers
sudo a2enmod deflate
sudo systemctl restart apache2

1. Open the main Apache configuration file:

sudo nano /etc/apache2/apache2.conf

or, if you are working with virtual hosts:

sudo nano /etc/apache2/sites-available/your-site.conf

2. Add the following directive to specify the Vary: Accept-Encoding header:

<IfModule mod_headers.c>

    Header append Vary: Accept-Encoding

</IfModule>

3. If gzip compression is enabled, ensure it works with Vary:

<IfModule mod_deflate.c>

    AddOutputFilterByType DEFLATE text/html text/plain text/css application/javascript application/json

    Header append Vary: Accept-Encoding

</IfModule>

4. Save the file and exit.

If you do not have access to the server configuration files, you can modify the .htaccess file in your website root directory.

1. Open or create a .htaccess file:

nano /var/www/html/.htaccess

2. Add the following lines:

<IfModule mod_headers.c>

    Header append Vary: Accept-Encoding

</IfModule>



<IfModule mod_deflate.c>

    AddOutputFilterByType DEFLATE text/html text/plain text/css application/javascript application/json

    Header append Vary: Accept-Encoding

</IfModule>

3. Save and close the file.

After making changes, restart Apache to apply the new configuration:

sudo systemctl restart apache2

1. Ensure gzip or Brotli compression is enabled for your website.
2. Example configuration for gzip in Apache:

<IfModule mod_deflate.c>

    AddOutputFilterByType DEFLATE text/html text/plain text/css application/javascript application/json

</IfModule>