A software that collects system performance

The system network architecture is like so. The firewall rules only allow ingress connection and not vice versa

A1 -> A2 -> A3

B2 -> B2 -> A3

C2 -> C2 -> A3

…

All x2 server can connect to A3

We need to design a program that can collect x1 and x2 and send to A3 to send to the internet

My ideas is setting up a a controller on A3 and install agents on all server to send data to A3

3rd party software not allowed