best varnish architecture for high concurrency site

[Hernán Marsili]

Hi,

We are 'playing' with different architecture options to maximize the usage
of Varnish Cache. We currently have 6000 concurrentes users and we are
balancing over 4 servers. Each server has a Varnish, (4gb malloc) which
consumes a local backend with Apache / Tomcat (another 4gb). Every box is a
virtual machine with 8gb RAM and 4 vcpu.

We build it that way because we need PERSISTENT CONNECTIONS to the backend
on Varnish bypass. We have strong dynamic functionality.

We think that having 1 big Varnish (dedicated use) and balance all the
connections to the dedicated backends will serves us best. Basically, we
will improve varnish caching, reduce the petitions to the database (now we
have 4 servers asking the same to the DB) and will also reduce connections
and resources on the backend servers.

Questions:
a) what do you think of each scenario?
b) it is possible to balance connections persistently to the backend
servers?

Regards,
Hernán.
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