Health monitoring question

What is the pool member?

http will only test that port 80 is available and responding with http responses. for an all-ports server, gateway-icmp is probably better.

If it is a router address, then gateway-icmp pinging through the router to a device beyond the router is recommended (Transparent monitor with an Alias address).

No monitors are required on a pool. They are an option that can be used to make sure the services delivered from the pool members are being delivered correctly. You can use as many monitors as you would like to achieve the appropriate health status analysis but, of course, there is the potential for a performance impact. There is also the question of monitor effectiveness. The gateway-icmp monitor is a service check monitor (although it really only checks the IP address to make sure it is reachable). It does not check to ensure the address is serving the correct content. An HTTP monitor is a content check monitor, meaning it is designed to send an HTTP request to the monitored pool member, and then confirm that the response received is what was expected. It is a far more robust monitor than an address check monitor, assumed it is used correctly. If you are serving more than just HTTP content from the pool, then you might want to incorporate multiple content check monitors. You can also adjust how many monitors have to succeed in order for the pool member to be marked up. Of course, I'm just brushing the surface of monitors here. Have you taken any training from F5 on using monitors? There is a lot to learn - more than can be described here, most likely.