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Invalidating Varnish automatically with the Dropsolid Purge module

Your environment runs Varnish in front of your Drupal application. You can always clear the whole cache by hand, but for a Drupal site you usually want the cache to invalidate itself the moment content changes, and only for the pages that were affected. The Dropsolid Purge module does exactly that: it connects Drupal's cache-tag system to Varnish, so editing a node, term or menu clears just the cached pages that reference it, across every load balancer in front of your environment.

This is different from the manual "Clear Varnish" action, which empties the entire cache in one go. See Clearing your application's Varnish cache for that.

What the module does

  • Invalidates Varnish by cache tag, so only the pages affected by a change are cleared instead of the whole site.
  • Supports a full "everything" invalidation for the cases where you do want to clear all of it.
  • Works across multiple load balancers.
  • Scopes invalidation to your site with the X-Dropsolid-Site header, so sites that share a Varnish never clear each other's cache.

Before you start

Install the module

Install Dropsolid Purge the same way you install any other Drupal module. If you need a refresher, follow Drupal's own guide: Installing modules. With Composer that is:

composer require drupal/dropsolid_purge

Then enable it from the Extend screen or with drush en dropsolid_purge.

Configure it

The configuration steps (adding the purger at /admin/config/development/performance/purge and the settings.php block) are documented in the module's README. Follow those instructions there so you are always working from the current version: Dropsolid Purge on Drupal.org.

Two things to keep in mind while you follow the README:

  • We recommend enabling both the cron and the late runtime purge processors for the fastest invalidation.
  • In the load balancer configuration the IP is 127.0.0.1, which matches the README example. The one value you set per environment is the port (see "Find your Varnish port" below). In the rare cases where your environment uses a different IP, we tell you through the support desk.

Find your Varnish port

The port for the load balancer configuration comes from your own environment:

  • Open your project in the platform and go to the environment you are configuring.
  • Open the Services tab; the Varnish info is listed there.
  • Use the port shown in the load balancer entry. Keep the IP at 127.0.0.1 unless we have told you otherwise via the support desk.
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