How to create a vpn site-site with openvpn docker and VPS?

[Poltsie]

First a little background information:

For our customers I am trying to create a network monitor service with libreNMS (running on a VPS). With libre I want to monitor network devices on the LAN.

So my intention is to run a openvpn server in a docker container on the VPS. I do this because the VPS is running a libreNMS configuration. (https://github.com/kylemanna/docker-openvpn) and let a raspberry pi (client) connect to the openvpn server. I want to create for every customer a client that connects to the vps.

Now the problem:

I got the openvpn server running and the client running. From the client I get a succesfull connection, that is good. But from there I want to create a route back to the client (site-site). But from there I dont understand how to do this. I tried to follow the following articles, without succes:

https://openvpn.net/vpn-server-resource ... in-detail/

https://openvpn.net/community-resources ... er-subnet/

Normaly I create site-site connections from router to router with sonicwall devices, but the vps is hosted elsewhere with one IP address on one interface. It does not have a internal network.

What I want:

I want to create a route from the VPS to the lan subnet of the client.

* The openvpn server has for example IP address: 1.1.1.1 (one WAN IP)
* The client has for example WAN IP address: 2.2.2.2 for example LAN subnet 3.3.3.0/24