best varnish architecture for high concurrency site

Hernán Marsili hernan at
Thu Feb 20 15:10:39 CET 2014

Hi John,

Thank you very much for you quick response. To be honest I don't have a
measure right now of how many connections produces this 6000 concurrent
users. I will measure it on the next rush hour. Currently, is distributed
along 4 servers. On average, each servers has 1000 connections.

a) we know that, we are think on an identical box to maybe balance it or
have it as spare
b) we need that each users are consistently served from the same backend
server. If not, they will appear logged in on 1 server but not the others.

Bottom line, do you think 1 Varnish balancing against 3 backends is best
than having 4 varnish balancing 1 to 1 with a backend?


On Thu, Feb 20, 2014 at 10:58 AM, John Cihocki <john at>wrote:
>> How many concurrent client connections do those 6000 concurrent users
>> generate? You'll need to make sure you have enough available worker threads
>> to accommodate those users plus extra to soak up traffic spikes, ideally.
>> a) One thing to consider with a single instance architecture is the lack
>> of redundancy. If that host goes down, your site is down.
>> b) Do you mean have persistent client connections to backend, like
>> websockets? Or have varnish make backend requests through persistent
>> connections. The former is possible, the latter is the default behavior as
>> I understand it -- Varnish will always attempt to reuse an existing
>> connection for the next backend request.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the varnish-misc mailing list