In BIG-IP LTM, health monitors are used to determine the availability of pool members and directly influence traffic flow decisions in the data plane.
Key characteristics of the default HTTP monitor according to BIG-IP Administration Data Plane Concepts:
Sends an HTTP request (typically GET /)
Expects an HTTP response code of 200 OK
Any response other than 200 is treated as a monitor failure
A failed monitor causes the pool member to be marked offline (down)
In this scenario:
Two pool members return 404 Not Found
A 404 response indicates that the requested object was not found
This does not meet the success criteria of the default HTTP monitor
These two members are therefore marked offline
One pool member returns 200 OK
This matches the expected response
The member is marked online
Resulting Pool Member Availability:
2 members: Offline
1 member: Online
Why the Other Options Are Incorrect:
B – 404 responses are not considered healthy by the default HTTP monitor
C – At least one member responds with the expected 200 OK
D – Members returning 404 responses fail the monitor and cannot be marked online
Key Data Plane Concept Reinforced:
BIG-IP health monitors make binary availability decisions based strictly on configured success criteria. For HTTP monitors, response codes matter—404 is a failure, even if the service is technically reachable.
===========
