Apache CDN Setup with mod_cdn

apache cdn

There are various CDN integration methods available to users depending upon which CMS or Framework is being used. However, if you are an Apache user, you can also integrate a CDN directly into your web server with a module called mod_cdn. Once installed and configured, this module allows you define which asset types you want to accelerate by rewriting the origin URL with a CDN URL. You can also get quite granular regarding which directory / assets you would like to accelerate. This is because the configuration is specified within your Apache’s configuration file, therefore providing lots of flexibility.

Configuring Apache CDN with mod_cdn

The following section outlines the steps required to install and configure the Apache mod_cdn module in order to setup an Apache CDN combination.

  1. Ensure that you have the following libraries installed on your server. Otherwise, the mod_cdn module may not work as expected.
    sudo apt-get install libxml2-dev libapr1-dev apache2-dev libssl-dev
  2. From your CLI, download the mod_cdn module with the following snippet and change into the mod_cdn-1.1.0 directory once the file has been unzipped.
    wget http://agile.internap.com/assets/mod_cdn-1.1.0.tar.gz
  3. Compile the mod_cdn from source against Apache 2.2.7 or higher.
  4. Copy mod_cdn.so to the following directory /usr/lib/apache2/modules/. Additionally, ensure that the cdn.load file contains the following:
    LoadFile /usr/lib/libxml2.so.2
    LoadFile /usr/lib/libssl.so.0.9.8
    LoadModule cdn_module /usr/lib/apache2/modules/mod_cdn.so
  5. Now, we need to copy the cdn.load and cdn.conf files into the /etc/apache2/mods-available/ directory with the following command.
    cd /etc/apache2/mods-enabled
    cp cdn.load /etc/apache2/mods-available/
    cp cdn.conf /etc/apache2/mods-available/

    Then, link them from mods-enabled with the following.

    ln -s ../mods-available/cdn.conf cdn.conf
    ln -s ../mods-available/cdn.load cdn.load
  6. There are a variety of Apache directives that can be used within your configuration file to properly deliver the desired static assets from the CDN instead of the origin server. You must define the following snippet within the <VirtualHost> if you want to rewrite all of your site’s static assets to use the CDN URL. However, you can also specifically define a set of directives for a particular directory if you do not want to accelerate the entire website.
    <IfModule mod_cdn.c>
    CDNHTMLToServer https://cdn.yourwebsite.com
    CDNHTMLFromServers https://yourwebsite.com
    CDNHTMLRemapURLServer \.png$ i
    CDNHTMLRemapURLServer \.jpg$ i
    CDNHTMLRemapURLServer \.gif$ i
    CDNHTMLRemapURLServer \.css$ i
    CDNHTMLRemapURLServer \.js$ i
    CDNHTMLLinks img src
    CDNHTMLLinks link href
    CDNHTMLLinks object data
    CDNHTMLLinks input src
    CDNHTMLLinks script src
    CDNHTMLLinks a href

The snippet above enables the Apache CDN configuration by telling the server which extensions should be replaced. The CDNHTMLToServer directive corresponds to your CDN’s Zone URL (e.g. lorem-1c6b.kxcdn.com) or Zonealias (e.g. cdn.yourwebsite.com). The CDNHTMLFromServers corresponds to your origin domain. The CDNHTMLRemapURLServer directive defines the extensions for which you want to accelerate. Finally, the CDNHTMLLinks directive defines the tag / attribute pair for which the module expects to find links to content in order to replace them.

Once you have defined the snippet from step 5 in your Apache’s configuration file, save your changes and restart Apache with the following command service apache2 restart. Once Apache has restarted, go to your website and view the page source to ensure that the static assets you have defined are being properly rewritten to reflect the CDN URL.


      1. Eugene Kalashnikov

        Thanks for the question. The extension mod_cdn.so should be compiled from the source. The article is corrected accordingly.

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