RpcEndpointRef — Reference to RPC Endpoint
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
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
3) - the number of times to retry connection attempts.
3s) - the number of milliseconds to wait on each retry.
It also uses lookup timeouts.