Microsoft Exchange Server 2013: Connectivity, Clients, and UM

The death of affinity

Another very important side effect of the decoupling of the CAS and Mailbox roles is a sharp reduction in the need for client affinity. Affinity means that a session for a given client remains with the same CAS for the duration of the connection. In other words, after a client connects to a particular CAS, the same CAS would continue to service the connection until the connection is terminated. To do this, the CAS must maintain session state so that any load balancers in the path know which CAS handles which connection. Sessions or protocols in which client affinity is maintained are said to be sticky. If a load balancer or reverse proxy solution doesn’t support affinity, it will break some Exchange 2007 and Exchange 2010 ...