F5 Node monitor vs pool monitor
May 4, 2018
F5 health monitors can be used to monitor nodes and pool memebers.
What is relation between them? What if you configure the node monitor as icmp and and pool monitor as http and system administrator disable icmp on the node (on the server firewall)? In this case there is a conflict – node monitor indicates that node monitor is down, but pool monitor should indicate that a pool member is still up (the service works regardless icmp was disabled)!
However, it doesn’t work like that. If node monitor is down then pool member is also down (regardless that service still works in reality). Of course Virtual Server is also down. The following pictures shows this situation – there are three nodes (they doesn’t reply to node icmp health monitor), the services works [http] but the pool members are in offline state.
It is worth to notice what happens if node has no monitor. If I disable the health monitor for node 10.0.2.103 the icons status change respectively.
One more note – node monitor is used to monitor “IP” or “server” and pool monitor is used to monitor “service”.
You can read more about nodes here: https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm-concepts-11-4-0/4.html