Varnish HA and MediaWiki HTTP PURGEs

[Justin Lloyd]

Hi all,

I just saw the new Varnish HA 
video 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. 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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Re: Varnish HA and MediaWiki HTTP PURGEs

[Guillaume Quintard]

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  wrote:

> Hi all,
>
>
>
> I just saw the new Varnish HA video
>  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
> . 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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> varnish-misc mailing list
> varnish-misc@varnish-cache.org
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>
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RE: 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 
Sent: Monday, June 14, 2021 7:54 AM
To: Justin Lloyd 
Cc: varnish-misc@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 
mailto:just...@arena.net>> wrote:
Hi all,

I just saw the new Varnish HA 
video 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. 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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