Probing to see if Varnish is Alive.

[Michal Taborsky - Netretail Holding]

  Hi Mohan,

here is how we do it. We have also a couple of varnishes sitting in 
front of several backend servers. Each backend server responds to a 
simple http request on URL http://1.2.3.4/ping (1.2.3.4 being the 
backend server IP). We use this to check the backend server health in 
our VCL (in the probe statement). We also use this URL however to check 
the health of the varnish servers too. We just configured our load 
balancer to access the varnish URL (http://5.6.7.8/ping, 5.6.7.8 being 
the varnish IP address) and check it's http status code.

Now, the load balancer will stop sending traffic to the varnish server 
either when it is down itself or when all it's backends are down, which 
is essentially the same thing, because it means the varnish cannot serve 
traffic. We are using restart in the VCL to make sure that single 
backend failure will not trigger this. If one backend goes down, the 
ping request is served by different live backend.

Does it make sense?

Michal

Dne 15.9.2010 15:25, Mohan Rao napsal(a):
> Hi,
> Is there a way to probe a varnish server to see if it is alive ? We 
> have a couple of varnish servers that are load balanced. We would like 
> the load balancer to stop sending traffic to a particular varnish 
> server if we are updating that server. Is there a recommended way to 
> do this ?
> Thanks & Regards,
> Mohan
>
>
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-- 
Michal Táborský
chief systems architect
Netretail Holding, B.V.
http://www.nrholding.com

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