akka-docs/src/main/paradox/includes/cluster.md
For some use cases it is convenient or necessary to ensure only one actor of a certain type is running somewhere in the cluster. This can be implemented by subscribing to member events, but there are several corner cases to consider. Therefore, this specific use case is covered by the Cluster Singleton.
<!--- #cluster-singleton ---> <!--- #cluster-sharding --->Distributes actors across several nodes in the cluster and supports interaction with the actors using their logical identifier, but without having to care about their physical location in the cluster.
<!--- #cluster-sharding ---> <!--- #cluster-ddata --->Distributed Data is useful when you need to share data between nodes in an Akka Cluster. The data is accessed with an actor providing a key-value store like API.
<!--- #cluster-ddata ---> <!--- #cluster-pubsub --->Publish-subscribe messaging between actors in the cluster based on a topic, i.e. the sender does not have to know on which node the destination actor is running.
<!--- #cluster-pubsub ---> <!--- #cluster-router --->Distribute messages to actors on different nodes in the cluster with routing strategies like round-robin and consistent hashing.
<!--- #cluster-router ---> <!--- #reliable-delivery --->Reliable delivery and flow control of messages between actors in the Cluster.
<!--- #reliable-delivery ---> <!--- #sharding-persistence-mode-deprecated --->@@@ warning
Persistence for state store mode is deprecated. It is recommended to migrate to ddata for the coordinator state and if using replicated entities
migrate to eventsourced for the replicated entities state.
The data written by the deprecated persistence state store mode for remembered entities can be read by the new remember entities eventsourced mode.
Once you've migrated you can not go back to persistence mode.
@@@
<!--- #sharding-persistence-mode-deprecated --->