As I understand L4 level load balancers, e.g. Azure Load Balancer, are almost alway stateless, i.e. they do not keep per-flow state on which server handles which TCP connection.
What is the behaviour of such load balancers in case of server additions to DIP pool? Do they lose some of the connections since corresponding packets get sent over to the new server?
Found Ananta: Cloud Scale Load Balancing - SIGCOMM paper which actually says that per-flow state is stored in one MUX machine (not replicated) which receives the associated traffic from the router. Hence server addition doesn't affect existing TCP connections as long as MUX machines stay as is.