Adding multiple servers to a zone will distribute requests evenly between all servers. Requests are routed based on the client IP address and the number of servers in the zone.
Adding or removing servers from a zone will cause all traffic to be distributed.
To stop routing requests to a server, set it to inactive. Only traffic that would have been routed to that server will be redistributed among the remaining servers.
There is no warm up or adjustment period associated with the load balancer. It will respond immediately as demand increases or decreases.