Hi medmars,

You have two options:
The first option is to handle everything with Nginx and do the forwarding / domain point there.
The second option is to use the built-in Odoo parameter '--db-filter'. With this filter you can 'link' databases to domains.
A quote from the official documentation:

--db-filter <filter>
hides databases that do not match <filter>. The filter is a regular expression, with the additions that:
%h is replaced by the whole hostname the request is made on.
%d is replaced by the subdomain the request is made on, with the exception of www (so domain odoo.com and www.odoo.com both match the database odoo)

You can find the official docs here: https://www.odoo.com/documentation/8.0/reference/cmdline.html and there is a nice tutorial here: https://www.inlinetechnology.com/blog/howto-3/post/odoo-mapping-url-to-database-10

Yenthe