Choosing a monitoring system: is a cascade structure possible?

Question

Monitoring

It is necessary to monitor servers and computers in several organizations.
Installing one monitoring system and doing dozens of port forwarding in each organization to get to each computer is rather inconvenient.
So far, I have come up with this option: set up an independent monitoring system in each organization, as well as another one - on an external resource for all of them, which will receive data from all.
So that you can see the big picture in one place. For you can set up notifications in each organization separately, but it will be tedious to regularly view everyone individually.
Please tell me which of the monitoring systems like Zenoss, Nagios, etc. able to line up in such a cascade?
Or maybe there is a more elegant solution for my situation?
upd (picked up from a comment):
WHAT I want to monitor: vital parameters (disk status, memory and processor load, temperatures) of servers and workstations (mainly Win, there are servers and Linux), the status of services and preferably events and logs from servers
AS I want monitor - this is me now and I'm trying to solve for myself
external IP in organizations - there are options without a static address.

Answer 1

There is a zabbix proxy in zabbix, you can deploy it on the router or forward only one port

Answer 2

Options 100500
1) From VPN (without changing the gate)
2) To reverse sssh tunnels, if there is no white ip
The main question is WHAT and HOW are you going to monitor specifically

Answer 3

Zabbix.
If the system is large - contact.

Answer 4

Look in the direction of Dude from Mikrotik, though there will have to be a lot of settings for your tasks, but there is a cascade.

Answer 5

If anyone is interested...
On my own, I also found that Nagios, through a certain module (unfortunately, I didn’t make a note to myself) can depict a Zabbix proxy similar to Zabbix.
However, some crutch of such a solution in Nagios and the need to configure it through a bunch of config files, as well as the absence (maybe due to my ignorance) of other alternatives pushed me towards Zabbix.
Haven't tried Zabbix proxy yet. While I master system on a local area.