I have a client whose site grinds to a halt every time they send out a mailing because of incoming traffic. We're using Varnish without SSL endpoint termination, so right now, we're not caching those pages at all.

However, even if we install SSL endpoint termination (or use HTTP links), the click-through links are unique, even though they return identical content. Is that content cacheable by Varnish? Or does using unique click-through links completely break caching?

1 Answer 1


So, only the civicrm click-through requests are grinding the VM/Server?

I am not seeiing how to cache those without breaking the counter functionality.

Is site OK when not using the click-through functionality? To make 100% sure that those are the cause, and not some other Varnish config (like not caching when certain session cookies are available).

If it is really the CiviCRM counter functionality and not the pages it forwards to and you need that functionality then I only see 2 options:

  • upgrade the server/VM
  • send the mailing in batches (maybe even spread over a few days)

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