Session state availability means that data associated with a user session is not lost during a service failover. When a service failover occurs, the session state data that is stored by the failed instance is made available to the failover instance. This mechanism is known as session failover. The result is that the service failover is transparent to the user: the user will not be required to log in again or to restart a business operation.
Session failover is supported in the reference configuration through two mechanisms:
Access Manager session failover. Access Manager session information is created when a user is authenticated and stored in a replicated database. This database is shared by Access Manager instances and accessed through Message Queue. If an Access Manager instance fails, the load balancer routes all user requests to a failover instance (service failover). The failover instance retrieves session information from the shared database and maintains the session.
Portlet session failover. The JSR 168 portlet specification requires portlets to map state information to an HTTP session. If a web container supports highly available HTTP sessions, and if a Portal Server instance fails, the HTTP session state can be recovered by the failover instance. In the reference configuration, Portal Server is deployed in an Application Server cluster, in which High Availability Session Store (HADB) is used to store and replicate portlet session state. The failover instance retrieves session information from HADB and maintains the session.
Portlet session failover requires availability of Access Manager session state. An Access Manager failure could therefore interfere with portlet session failover, unless Access Manager session failover is also implemented.
When a user is successfully authenticated with Access Manager, the browser is redirected to a Portal Server instance. A portal desktop session is created on this instance and is mapped to the user's Access Manager session. This portal desktop session is used to track Portal Server specific information such as the user's merged display profile and provider properties. If a Portal Server instance fails, the desktop session is automatically re-created by using the user's display profile and attributes that are stored in the Access Manager's user session. However, provider properties that are stored in local memory are lost.