multiple backend + apache bottleneck

[Denis Brækhus]

----- jean-marc pouchoulon <jean-marc.pouchoulon at ac-montpellier.fr> wrote:
> Hello all ,
> We are using zope/nuxeo cps  with 8 zeo clients and I test varnish 1.3
> in place of squid 2.6.
> squid uses 8 zeo peers and if I've understood well varnish can  have 
> "only one" host per backend.
> is there is a way to load balance upon multiples hosts with varnish ?

There are multiple ways to achieve this, but nothing is built into varnish (yet atleast). But there are multiple solutions out there you could utilize, either proprietary appliances or software (Alteon/Radware/Cisco/Zeus XTM) or open source solutions. I would guess the latter is most interesting for you, and I have heard good things about perlbal [1]. It is used by a number of high profile, high load sites. 

We are currently running a setup where the pool is divided like this:

           Alteon LB 
           /       \
VarnishServer1     VarnishServer2
       |                  |
Apache2+mod_php1   Apache2+mod_php2

This caters to multiple failure situations; whenever Apache1 goes down Varnish2+Apache2 will serve the load and vice versa. If Varnish1 or Varnish2 goes down, the Alteon will direct traffic straight at the relevant backend (through a backup server config setting), but with a lot less weight than the remaining VarnishServer.

Ideally we would like to build an even more efficient setup, but there are certain limitations of the LB Switch OS we are currently running that prevent this as of now.

The setup I described above is probably not suited to your application though, this was more of an elaboration on one way to setup loadbalancing with Varnish.


[1] http://www.danga.com/perlbal/

-- 
Denis Braekhus - Teknisk Ansvarlig ABC Startsiden AS
http://www.startsiden.no