In any SaaS or web application, incoming traffic from end-user, normally hit a load balancer as the first tier. The role load balancer is to balance the load of the request to next lower tier. There are two types of load balancers such as software-base or hardware based. Most load balancers provide different rules for distributing the load. Following are two of the most common options available.

• Round Robin: With round robin routing, the load balancer distributes inbound requests one at a time to an application server for processing, one after another. Provided that most requests can be serviced in an approximately even amount of time, this method results in a relatively well-balanced distribution of work across the available cluster of application servers.The drawback of this approach is that each individual transaction or request, even if it is from the same user session, will potentially go to a different application server for processing.

• Sticky Routing: When a load balancer implements sticky routing, the intent is to process all transactions or requests for a given user session by the same application server. In other words, when a user logs in, an application server is selected for processing by the load balancer. All subsequent requests for that user are then routed to the original application server for processing. This allows the application to retain session state in the application server, that is, information about the user and their actions as they continue to work in their session.Sticky routing is very useful in some scenarios, for example tracking a secure connection for the user without the need of authenticating repeatedly with each individual request (potentially a very expensive operation). The session state can also yield a better experience for the end user, by utilizing the session history of actions or other information about the user to tailor application responses.Given that the load balancer normally stores only information about the user connection and the assigned application server for the connection, sticky routing still meets the definition of a stateless component.