Server Monitoring through firewall, vpn etc

[ncjbhd]

Hey Guys,


I am looking to monitor multiple servers for multiple clients.

Some clients servers are behind vpn, some are behind proxy etc etc... my client don't want to open any ports.

Would it be possible that an agent or daemon or something similar that would communicate the polling results to the main monitoring server through http?

I already found Server density but i am looking for something open source. i really like zenoss


thanks a lot