HA with Varnish? advice request

[Allan Wind]

On 2011-12-07 00:05:24, Alejandro wrote:
> Hi guys,
> 
> I need your advice... I'm using varnish into multiple server, some for
> caching dynamic content and other only for static content.
> 
> On front of the Dynamic Content Varnish y have Cisco ACE Load balancer, but
> on front of the Static Varnish, the traffic is much higher and can't use
> Cisco ACE, for this reason I'm using RoundRobin DNS into this 2 servers.
> 
> This week I had, some network issue with one of this servers and when the
> network go down I loose 50% of the traffic...
> 
> here my question, or advice request... How I can have HA with 2 varnish
> server? I'm thinking on Heartbeat or Heartbeat+ldirectord, please fell free
> to send your suggestions.

As your clients do not fall back to the 2nd IP it means you need 
one (active/passive) or two vips (active/active) that can be 
shared between your two varnish servers.

If you have cachable dynamic content then your two Varnish 
instances may return different content to the same client.  This 
may or may not be an issue.  Others will have to weight in if 
cache invalidation of Varnish entries is a doable strategy 
(if you cannot set your expiration headers correctly).  On the 
positive side you have a warm cache should one of your Varnish 
instances fail.  With a active/passive fail over the cold cache 
may be problematic.

That said I am surprised that you think Varnish will be able to 
handle your traffic but a pair of load balancers cannot.  If the 
Cisco ACE is not up to it have you looked at haproxy?  You still 
have the same vip issues, but load balancers are stateless and 
give you persistence connections to minimize differences between 
Varnish instances.


/Allan
-- 
Allan Wind
Life Integrity, LLC
<http://lifeintegrity.com>