Problem

Admin node manager is not responding. Choosing any option under the managedomain --menu throws an error:

Error: The node manager on https://<ipv4>:8090/api is not running. Please start it and retry this command

Also the page to Node manager is not opening even if the port is opened and NM is listening to the port.

The problem occurs on RedHat where the default Iptables rules have this set:

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 REJECT all -- * * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT 1339 packets, 158K bytes)
pkts bytes target prot opt in out source destination

iptables -vnL
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
1683 123K ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
5 420 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0
17 1020 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0
1 52 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
1766 183K REJECT all -- * * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited

If you run network capture on the loopback address you will see ICMP packets like this:

16:20:20.330365 IP apigw.somedomain.com > apigw.somedomain.com: ICMP host 192.168.1.2 unreachable - admin prohibited, length 56

Resolution

You need to run "service iptables stop" to unload the rules and fix the problem.