LB_FAILED is triggered when LTM is ready to send the request to a pool member and one hasn’t been chosen (the system failed to select a pool or a pool member), is unreachable (when no route to the target exists), or is non-responsive (fails to respond to a connection request).
when LB_FAILED {
LB::reselect pool ANOTHER_POOL
}
If you use this rule in Pool_1 and all Pool_1 members are off or unreachable or the connectil limit has been reached you can redirect the client to Pool_2 (ANOTHER_POOL in the above example)