RpcEndpointRef is a reference to a RpcEndpoint in a RpcEnv.

RpcEndpointRef is a serializable entity and so you can send it over a network or save it for later use (it can however be deserialized using the owning RpcEnv only).

A RpcEndpointRef has an address (a Spark URL), and a name.

You can send asynchronous one-way messages to the corresponding RpcEndpoint using send method.

You can send a semi-synchronous message, i.e. "subscribe" to be notified when a response arrives, using ask method. You can also block the current calling thread for a response using askWithRetry method.

It also uses lookup timeouts.