Nimbostratus
MVP1) Does the action on service down feature work when the whole server is down? Or does it work when each server is down?
The Action On Service Down feature allows the BIG-IP system to choose another pool member and rebind the client connection to a new server connection if the target pool member becomes unavailable.
2) If I force down one server, does action on service down work?
yes
2-1)If it works, LTM send RST directly to the client and server side of the server that has been force-downed? Immediately?
if you selected reject // The BIG-IP system sends RST or ICMP messages to reset active connections and removes them from the BIG-IP connection table. If there are available pool members for the connection, the BIG-IP system resets and clears the active connections but sends subsequent newly arriving connections to the available pool member and does not send RST or ICMP messages.
2-2) Is the session table will be deleted of the force down server immediately?
yes, if you selected reject or drop
please check below url