The last tab in the External Cache Control configuration deals with Varnish in particular. While this should not need to be modified ever, there are some scenarios where the settings could require modification (changing your site’s domain for example). Follow the instructions in the section Clearing the caches for a specific URL to access the External Cache Control configuration page, then click on the “Varnish” tab to manage the Varnish settings. Use caution in modifying these settings as you can potentially interfere with the operations of other sites.
A series of IP addresses, one per line
This is the array of Varnish servers that will be targeted by the system. You should never need to change these.
A series of host names, one per line
When we wipe the cache for a URL, we target multiple hosts for each URL in Varnish. This is because sites can often be accessed using multiple domains and we must make sure that all of them get cleared. Only use the domains that are used by your site.
A series of URLs, one per line
When we wipe the entire cache for the site, we use these URLs to issue the request (it is a BAN request to Varnish). Every page that starts with any of the given URLs will be wiped.