Purge Module Invalidating Varnish Too Frequently

Issue

When the acquia_purge module has been implemented the way Guide to Acquia Purge and Akamai CDN Caching on Acquia Cloud Platform, some customers may run into an issue where the varnish cache is being invalidated with unmanageable frequency.

Resolution

Blacklist Problematic Tags from Purge's Core Tags Queuer

Most commonly the tags which are causing this problem are node_list and views_data. Whichever tags may be at fault, the process is the same. Open your site's Purge configuration at the path: 

/admin/config/development/performance/purge

Then, from the "Core tags queuer" dropdown menu, select "Configure."

From the resulting dialog box, click the "Add prefix" button.

Finally, add the new tags to the list and then click on the "Save configuration" button.

This should stop those specific tags from invalidating your site's Varnish cache.

On the backend this is a configuration change to purge_queuer_coretags.settings. Be sure to follow your site's configuration management protocols to safely make this change in your production environment.