Strategies for splitting load across varnish instances? And avoiding single-point-of-failure?
michael at dynamine.net
Sat Jan 16 03:14:43 CET 2010
On Fri, Jan 15, 2010 at 5:33 PM, pub crawler <pubcrawler.com at gmail.com>wrote:
Varnish performs very well. Extending this to have a cluster
> functionality within Varnish I think just makes sense.
haproxy and F5 equipment also both perform very well.
> The workaround
> solutions so far seem to involve quite a bit of hardware as well as
> having a miss rate of 50% in example of 2 Varnish instances. Sure it
> can hot populate fast, but it's two stacks of memory wasted for the
> same data per se.
If you hash your requests from a load balancer across a pool of n varnish
instances, the most you lose in the event of a failure is 1/n. You don't
cache objects in more than one instance. There's no "wasted" memory.
I suppose a custom solution to hash the inbound
> requests somehow and determine which Varnish should have the data can
> be done, but unsure if anyone now is doing that.
That's precisely what L7 switches do. As David said, haproxy has this
functionality, as do other implementations.
> Squid is a total disaster. If it wasn't none of us would be here
> using Varnish now would we :) It's amazing Squid even works at this
Can you quantify this statement? Squid works very well at some
It's not like the code that was out there working spontaneously started to
> I put in a feature request this evening for this functionality. We'll
> see what the official development folks think. If it can't be
> included in the core, then perhaps a front-end Varnish proxy is in
> order developmentally. I'll say this akin to Moxi in front of
> memcached instances: http://labs.northscale.com/moxi/
I'm all for putting backend hashing into Varnish for the purpose of routing
requests to backends based on a consistent hash of the request parameters --
and there's no reason why the backend can't be another Varnish instance.
But the appropriate use of this is to more efficiently utilize cache memory
by associating an object with a designated Varnish server in a pool, not for
HA. This was one of my first requests that still (alas) has seen no
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