How it works...

OpenDaylight clustering heavily relies on AKKA technology to provide the building blocks for the clustering components, especially for operations on remote shards. The main reason for using AKKA is because it suits the existing design of MD-SAL, as it is already based on the actor model.

OpenDaylight clustering components include:

• ClusteringConfiguration: The ClusteringConfiguration defines information about the members of the cluster, and what data they contain.
• ClusteringService: The ClusteringService reads the cluster configuration, resolves the member's name to its IP address/hostname and maintains the registration of the components that are interested in being notified of member status changes.
• DistributedDataStore: The DistributedDataStore is responsible for the implementation of the DOMStore, which replaces the InMemoryDataStore. It creates the local shard actors in accordance with the cluster configuration and creates the listener wrapper actors when a consumer registers a listener.
• Shard: Shard is a processor that contains some of the data in the system. A shard is an actor, communicating via messages. Those are very similar to the operations on the DOMStore interface. When a shard receives a message, it will log the event in a journal, which could then be used as a method to recover the state of the data store. This one would be maintained in an InMemoryDataStore object.