You can use node indices to divide a cluster into subgroups, or subclusters, of a few nodes each. Using this configuration, each node in a subcluster shares session-state information only with other members of the subcluster. This approach requires a network traffic management solution to persist, or stick, user sessions so that each subsequent request from the same user is directed to the same set of nodes. The advantage of this approach is that cluster throughput scales more linearly, because the creation of an additional subcluster will not degrade the performance of any other group.
Additionally, this architecture does not support the SAML 2.0 single logout (SLO) profile using the SOAP binding. If one or more SAML 2.0 connections are configured to support SLO via SOAP, you must choose between the sharing all nodes and designating state servers deployment strategies in directed clustering.
The following diagram illustrates the subcluster approach.
In this example, the preferred.node.indices property of each server in the cluster lists the indices of all nodes in its subgroup (including itself). Requests are directed to all nodes but the load balancer directs user sessions to the same subcluster.