Sticky Session VS Session Replication

Sticky Session

In a load balanced server application where user information is stored in the session, it will be required to keep the session data available to all machines. This can be avoided by always serving a particular user session request from one machine.

The machine is associated with a session as soon as the session is created. All the requests in a particular session are always redirected to the associated machine. This ensures the user data is only at one machine and load is also shared.

Session Replication

Session replication is used in application server clusters to achieve session failover. A user session is replicated to other machines of a cluster, every time the session data changes. If a machine fails, the load balancer can simply send incoming requests to another server in the cluster. The user can be sent to any server in the cluster since all machines in a cluster have a copy of the session.

Session replication may allow your application to have session failover but it may require you to have extra cost in terms of memory and network bandwidth.