Using Varnish for full-page cachingfor Drupal 8 , 9 , 10 , and 11

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8.x , 9.x , 10.x , 11.x

Building on our understanding of advanced server optimizations, this lesson introduces you to Varnish, a powerful HTTP-accelerator designed for high-traffic and dynamic sites. Varnish acts as a reverse proxy that caches entire pages, significantly reducing server load and accelerating page delivery.

What is Varnish?

Varnish Cache is an open-source HTTP reverse proxy, commonly used to cache content-heavy web applications such as Drupal. Sitting in front of your web server, it caches HTTP responses fully, allowing subsequent requests to be served quickly from the cache rather than being reprocessed by the backend server.

Benefits of Using Varnish for Full-Page Caching

  • Speed: Dramatically improves page load times by serving cached content rather than generating it dynamically each visit.
  • Reduced Load: Offloads the webserver by intercepting and responding to HTTP requests, reducing dynamic page processing.
  • Scalability: Allows sites to handle higher traffic volumes efficiently, accommodating spike or consistent high load environments.

How Varnish Works

Varnish acts as a middleman between your users and the Drupal web server. When a user requests a webpage, Varnish checks its cache to see if there's a cached copy of the page:

  • If available, Varnish delivers the cached page immediately.
  • If not, Varnish forwards the request to the web server, caches the web server’s response, and then delivers the page to the user.

Setting Up Varnish for Drupal

Below is a step-by-step guide to install and configure Varnish for optimal performance with a Drupal setup.

Step 1: Install Varnish

Install Varnish on your server. For many Linux distributions, this can be done with a package manager:


# On Debian/Ubuntu
sudo apt-get install varnish

# On CentOS/RHEL
sudo yum install varnish

Step 2: Configure Varnish

Varnish uses VCL (Varnish Configuration Language) for configuration. Edit the /etc/varnish/default.vcl file to set up backend and caching policies:


vcl 4.0;

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}

Ensure your webserver listens on port 8080 instead of 80 since Varnish will handle port 80.

Step 3: Adjust the Varnish Service Configuration

Edit the systemd service configuration to specify the port Varnish should listen to:


# /etc/systemd/system/varnish.service.d/customexec.conf
[Service]
ExecStart=
ExecStart=/usr/sbin/varnishd -j unix,user=vcache -F -a :80 -T localhost:6082 -f /etc/varnish/default.vcl -S /etc/varnish/secret -s malloc,256m

Step 4: Integrate Varnish with Drupal

Configure Drupal to work seamlessly with Varnish. Drupal’s Cache Tags should be integrated into Varnish’s cache policies to handle purges efficiently.

Monitoring and Maintenance

  • Use Varnish’s built-in tools, such as varnishlog and varnishstat, to monitor cache usage and performance.
  • Regularly review caching rules in Varnish and update them based on your site’s traffic patterns and content update frequency.

Conclusion

Incorporating Varnish for full-page caching is a significant step towards optimizing performance, providing immediate loading improvements, and enabling your Drupal site to scale efficiently. By intelligently managing cache hits and responses, Varnish dramatically reduces server load while enhancing user experience.

What's Next?

In our next lesson, we’ll explore "Tuning Apache/Nginx for Drupal Workloads." This session will uncover server-specific optimizations tailored for Drupal environments, maximizing server response times and reliability. Join us to continue advancing your site's full potential!