You can select a few engine nodes as state servers. This deployment can be configured by setting the preferred-node indices of other servers in a group to those of the state servers. The load balancer should be configured to isolate the state-server nodes from end-user traffic. This approach scales better than the all-nodes approach because additional nodes do not require as much communication to every other node.
The following diagram illustrates the state-server approach.
In this example, the two state-server nodes have indices of 1 and 2; therefore, the preferred.node.indices property of the engine nodes handling requests would be:
And because the state servers are not processing transactions (based on the setup of the load balancer), the preferred.node.indices property for them is not used and can be left blank.