IIUC, you have two separate DCs with the same domain name? This is a bad situation
Support to multiple DCs is still limited to migration scenarios. In production environments, I recommend only a single DC per domain.
About the domain name, the best practice is pointed out in the manual: use a private subdomain of the public domain; i.e. ad.interlin.nl
, corp.interlin.nl
, home.interlin.nl
…
Users and groups — NethServer 7 Final
This could be viable. I’ve already seen similar deployments. I recommend only one DC: in your case it could be the VPS.
Did you see this Howto? You could grab the network configuration