The load balancer must support cookie-based or IP-based load balancing, which are sometimes referred to as layer-3, layer-4, or layer-7 load balancing. Hardware load-balancing devices are recommended. Software solutions, such as Microsoft's Network Load Balancing service, are also supported.
Some modules are not supported with both cookie-based and IP-based load balancing. See Module-Specific Load Balancer Requirements.
User-specific session state information must be maintained for each individual browser session within IIS's Web application memory. To maintain users' session state information, the load balancer must be configured to maintain a persistent session(also called client affinity or “sticky sessions”) with a specific server. When properly configured, client affinity forces the load balancer to direct all connections for each Web session to the same server machine that originally logged in the user.
For session persistence to work correctly in a cookie-based load balancing environment, the load balancer must generate the cookie used to determine which server the requests are delivered to. Using the ASP.NET_SessionID cookie for cookie-based load balancing is not supported and will produce errors if the request is generated on one server and then processed on a different server. OnBase supports RFC 2109 or RFC 2965-based cookies. Any cookies defined by load balancers must be in either of these formats to work correctly.
For more information about client affinity (or persistence), consult the load balancer's documentation.
Failover clustering of logged-in sessions is not possible due to session state persistence on the IIS Web server.