akka clusterclient

/**
* This actor is intended to be used on an external node that is not member
* of the cluster. It acts like a gateway for sending messages to actors
* somewhere in the cluster. From the initial contact points it will establish
* a connection to a [[ClusterReceptionist]] somewhere in the cluster. It will
* monitor the connection to the receptionist and establish a new connection if
* the link goes down. When looking for a new receptionist it uses fresh contact
* points retrieved from previous establishment, or periodically refreshed
* contacts, i.e. not necessarily the initial contact points.
*
* You can send messages via the `ClusterClient` to any actor in the cluster
* that is registered in the [[ClusterReceptionist]].
* Messages are wrapped in [[ClusterClient.Send]], [[ClusterClient.SendToAll]]
* or [[ClusterClient.Publish]].
*
* 1. [[ClusterClient.Send]] -
* The message will be delivered to one recipient with a matching path, if any such
* exists. If several entries match the path the message will be delivered
* to one random destination. The sender of the message can specify that local
* affinity is preferred, i.e. the message is sent to an actor in the same local actor
* system as the used receptionist actor, if any such exists, otherwise random to any other
* matching entry.
*
* 2. [[ClusterClient.SendToAll]] -
* The message will be delivered to all recipients with a matching path.
*
* 3. [[ClusterClient.Publish]] -
* The message will be delivered to all recipients Actors that have been registered as subscribers to
* to the named topic.
*
*  Use the factory method [[ClusterClient#props]]) to create the
* [[akka.actor.Props]] for the actor.
*
* If the receptionist is not currently available, the client will buffer the messages
* and then deliver them when the connection to the receptionist has been established.
* The size of the buffer is configurable and it can be disabled by using a buffer size
* of 0. When the buffer is full old messages will be dropped when new messages are sent
* via the client.
*
* Note that this is a best effort implementation: messages can always be lost due to the distributed
* nature of the actors involved.
*/