Oracle recommend the use of replication to provide high availability.
You can configure multiple master servers to store read-write copies of the same directories. For large-scale enterprise deployments, you must use multi-master replication.
You must establish a conflict resolution policy because updating the same directories in different master servers can cause conflicts.
For information about how to set up replica servers, see “Understanding the Oracle Unified Directory Replication Model” in Oracle® Fusion Middleware Administering Oracle Unified Directory and see “Replication” in the OpenLDAP Software 2.4 Administrator’s Guide.