I have raspberry pi with OpenVpn and Nginx installed on it. Both of them listen on TCP 443, but I enabled the "port-sharing" function in OpenVPN so the packages for Nginx arrive to it.
Now I try to monitor my website, lets say example.com with Netcat from another machine:
netcat -zv example.com 443
If I simulate an error (stop my Nginx) the TCP 443 is still open and answers the request from Netcat. No wonder, OpenVPN is still running. If I shut it down too, then I got the desired "connection refused" output from Netcat.
My question is: Can I specify the "type" of TCP package with Netcat, so it would skip the OpenVPN in to chain. OR Can you suggest me any similar, simple software to monitor the uptime of the example.com