Varnish is at it's most powerful when you replace the default 'vcl' with your own. By default, that's configured within /etc/varnish/default.vcl (debian).

You'll need to ensure your startup script references that file.

If you've got it open, you can see the default code. Basically, you need to 'unset' the Cookie header, as it's coming through the system, so that varnish can actually cache the item.

By default, you'll at least want to force static media (images, javascript, css) to be forced, akin to as follows:

sub vcl_recv {
    if (req.url ~ "\.(css|js|ico|png|gif|jpg|swf|jpeg|zip)$" ||
            req.url ~ "\.js?ver\=*$" ||
            req.url ~ "\.css?ver\=*$") {
                    unset req.http.cookie; # Cookies not needed here
                    return(lookup);
    }
}

The varnish documentation is really detailed, and goes into how to do basically everything you'll need to do in VCL. I'd strongly reccomend spending a few hours just reading over it:

Docs for v3: https://www.varnish-cache.org/docs/3.0/ v4: https://www.varnish-cache.org/docs/4.0/

Specifically, you'll probably want the 'User guide'.

Varnish is amazingly powerful, but you get out what you put in with it!

Good luck, if you get stuck on anything don't hesitate to ask more questions!

Don't know if you got the answer. But this is what you can do:-

1. Replicate the files example in folders like odoo, odoo1.
2. Go to any of the folder and start odoo server using different port like pass --xmlrpc-port=8000 in odoo folder and pass --xmlrpc-port=8001 in odoo1 folder that will run two different instances of odoo with different code-base. Also you can pass --dbfilter to restrict limited database access per port.