I'm quite new in shinken monitoring. I have 2 servers running virtual machines, on virtual machines are some web applications running, and one is psql database, and i need to monitor resources (CPU, RAM) and application servers (gunicorn) on them. The problem is that all virtual machines are behind NAT and monitoring should be on third server. I have only nginx web proxy for them, and.

To draw, in some way:

monitor/backup server ----> internet ---- > VM server ----> network ---> Virtual machines

My question is how to install and what to install on VM server so i can monitor those machines and have all on monitor/backup server?