This page shows three different SDN-R setup examples and the connectivity to other components.
Single (tiny setup)
For development of in case of small volume without any high availableity capability a singel ODL instance is sufficient.
OpenDaylight cluster (medium setup)
For production deployment are three node OpenDaylight cluster should cover most of the use cases.
Geo-Redundancy (full setup)
Based on use-cases and high availability requirements a geo-redundant setup with 2x 3 node local OpenDaylight cluster is shown in the figure below: