We have Odoo 12 (enterprise) on Ubuntu 18 running.

I want to force a database selection when a request comes from a certain domain (the webshop domain) 

So https://webshop.mydomain.com should only use the production "myproductiondb"

In /etc/odoo/odoo.conf I have set this:

server_wide_modules = base,web,dbfilter_from_header

proxy_mode = True

In Apache:

     ProxyRequests Off

     RequestHeader set X-Odoo-dbfilter "myproductiondb"

     #Redirect to ODOO

     ProxyPreserveHost On

     ProxyPass / http://localhost:8069/ retry=0

     ProxyPassReverse / http://localhost:8069/