1. A load balancer computer for configuring a load balancing program for a cluster of servers, the load balancer computer comprising: one or more computer-readable non-transitory storage devices and program instructions stored on at least one of the one or more storage devices, the program instructions comprising: program instructions to detect that the cluster cannot handle client requests with a predetermined level of performance, and in response, automatically request configuration information for another server that is not currently active in the cluster, to configure the load balancing program for adding the other server to the cluster to handle client requests; and program instructions to automatically configure the load balancing program for the cluster to add the other server to the cluster in accordance with the configuration information received for the other server, wherein the configuration information comprises a cookie affinity rule for sending different requests in a given session to a same server clone in a server group, subject to session affinity cookies being unique to each server in the server group, and wherein a load balancer configures the load balancing program for the other server based on the cookie affinity rule.