Thank you Francis for pointing the right direction.
If I understand correctly the documentation I should add
proxy_set_header Host $host;
considering I had the upstream server defined by: upstream webservers { server virt1:80; }
I tried it but had no luck with it, I also tried $http_host; and $proxy_host;
Also should I place this proxy_set_header before the proxy_pass ? I think yes, could you confirm this ?
Regards