Advanced Caching Part 2: Google Cloud CDN and Apache
In part 1, Google Cloud CDN and Varnish, we learned to cache dynamic responses. Here in part 2, we remove Varnish from the picture completely and do it all ourselves. Assuming Google Cloud CDN is up and running, we can use Apache to modify the HTML response before it gets cached.
1. Apache Module mod_substitute
Enable Apache Module mod_substitute on a Google Compute Engine (GCE) virtual machine (VM)
sudo a2enmod substitute
sudo service apache2 restart
NOTE: The above terminal commands are for Ubuntu Linux
2. Add the desired JavaScript code in a .js file
3. Use Apache Substitute to Insert a <script> Tag
Apache’s mod_substitute module allows you to write markup rules
vim /etc/apache2/ports.conf
In the ports.conf file, these markup commands let you leverage the Linux substitute command, “s”
Put the JavaScript file from step 2 inside the script tags
4. Make Rules for Different Directories and Files
Notice that the above substitution in the <Location> tag
The substitution is for all web pages in the web server’s root directory
Use additional <Location> tags for specific web directories and files
5. Response Body Modification Works!
The <head> tag in the HTML response was modified by Apache
It now includes a <script> tag referencing your JavaScript file
This is a great way to populate dynamic content in a cached web page*
*NOTE: Make sure to match your content’s expiration times with the life cycle of your .js file changes
