There are a number of reasons varnish could give a "Guru Meditation" error. Before proceeding with the steps in this guide, please ensure you have checked all the Magento and PHP-FPM logs for errors.
Error 503 Backend fetch failed Backend fetch failed Guru Meditation: XID: 65589 Varnish cache server
BogoHeader Header too long: Content-Security-Pol
In this case Varnish is complaining because the headers returned by Magento exceed the default limits.
In this case you will want to increase the following gradually until the error doesn't happen.
On your development instance, under Settings => Varnish, you should see Additional Service Arguments
Here are the values to copy
- `-p http_resp_hdr_len=95536k`
- `-p http_resp_size=169304k`
- `-p workspace_backend=8192k`
- `-p workspace_client=8192k`
Save the settings allowing MDOQ to recreate Varnish.
Repeat until resolved.