Load balancer requirements

In most production deployments, it is desirable to configure an external load balancer in front of the Endeca Server cluster hosting one or more data domain clusters. This topic discusses the considerations for this load balancer.

For the load balancer, the following considerations apply:

Include host names and ports of all Oracle Endeca Server nodes in the load balancer configuration.
If you add Endeca Server nodes to the cluster, you must update the configuration of the load balancer with the host names and ports of the added nodes.
You may optionally configure the load balancer to use session affinity. In this case, all queries from a given session are sent to the same Endeca Server node. This allows the Oracle Endeca Server to use its cache to avoid redundant processing of related queries.
Configuring session affinity also helps minimize consistency problems as updates propagate from the leader to the follower nodes in the data domain cluster (if you are not using outer transactions to run updates).

In addition, the Endeca Server cluster utilizes its own routing service, which also utilizes session affinity. The routing service recognizes requests sent from the same client and sends them to the same Endeca Server node that processed previous requests from the same client. (This assumes that the Endeca Server node is still hosting the Dgraph node for that data domain that can process the current request; otherwise, the request is sent to a different Endeca Server node.)