Varnish HA and MediaWiki HTTP PURGEs

[Justin Lloyd]

Thanks, Guillaume! I may follow up with you separately to discuss this in more depth since this could help with a redesign of our architecture that I’d like to do.

Justin

From: Guillaume Quintard <guillaume at varnish-software.com>
Sent: Monday, June 14, 2021 7:54 AM
To: Justin Lloyd <justinl at arena.net>
Cc: varnish-misc at varnish-cache.org
Subject: Re: Varnish HA and MediaWiki HTTP PURGEs

Hello Justin!

VHA is a commercial product, so we should probably keep it short of private as this is an open-source mailing-list.

However, since I'm sure the answer will be useful for other people, let's answer publicly :-)

VHA is a fire-and-forget tool, outside of the critical path so that replication requests failing (or being rate-limited) don't cause harm.
Purging, on the other hand, needs to be very vocal about failed purge requests failing as your cache consistency is at stake, so while VHA can do it, it's a bad idea.

However, VHA uses a tool named broadcaster which can be used on its own to do exactly what you need: replicate a single request for the CMS backend to the whole cluster, and report back so you can act on failures.

Cheer,

--
Guillaume Quintard


On Mon, Jun 14, 2021 at 7:39 AM Justin Lloyd <justinl at arena.net<mailto:justinl at arena.net>> wrote:
Hi all,

I just saw the new Varnish HA video<https://www.youtube.com/watch?v=KhqVdKe2RAU> and was wondering if VHA’s node synchronization would obviate the need for all of the Varnish nodes to be listed in the MediaWiki Varnish caching configuration<https://www.mediawiki.org/wiki/Manual:Varnish_caching>. MediaWiki uses the list of cache nodes to send HTTP PURGE requests to invalidate cached pages when they are updated. So with VHA, could MediaWiki just be configured with a single hostname or floating IP address (e.g. keepalived) that points to the Varnish cluster so that the cluster could handle replicating the PURGE requests?

Thanks,
Justin

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