How to monitor the load and status of a remote server?

Question

Debian

Hello. I was puzzled by the issue of monitoring remote servers.
In total there are about 20 computers running Windows and Debian. They are geographically distributed from each other, have an independent Internet connection. I'm interested in getting data about the state of the server (on / off), the load on the iron, readings from temperature sensors. Construction of graphs and reports for certain periods of time.
I looked towards Zabbix but could not get it to work with agents over the Internet. Tell me how you can close the Wishlist. Thanks

Answer 1

Zabbix is ​​still zabbix.
The most unpretentious agents only with him.
There is no static address at the branch - set up the "Active Agent". Yes, as a last resort, connect all branches to the monitoring point via vpn.

Answer 2

Nagios, zabbix
A server (virutalka, in the sense) is usually set for such purposes. The principle of operation of any monitoring is that either the server polls agents (which may turn out to be proxies for server requests, passing them on), or the agents themselves look for the server and merge data to it.
For example, Nagios works according to this scheme. Nagios -> NRPE -> executing a request (which can include anything - even running a command to call another NRPE daemon) -> NRPE (returning data) -> Nagios