Load balancing of messages to cluster nodes based on cluster metric data.
It uses random selection of routees based on probabilities derived from
the remaining capacity of corresponding node.
the actor system hosting this router
decides what probability to use for selecting a routee, based
on remaining capacity as indicated by the node metrics
Pick the destination for a given message.
Pick the destination for a given message. Normally it picks one of the
passed routees, but in the end it is up to the implementation to
return whatever Routee to use for sending a specific message.
When implemented from Java it can be good to know that
routees.apply(index) can be used to get an element
from the IndexedSeq.