The SO_REUSEPORT socket option

CLUSTERIP shares one IP across multiple machines, doing a hash to make decide which machine gets the packet to userspace (they have the option of using the full 4-tuple or only part of it) You then use heartbeat or other clustering software to make sure that there is always some box that will handle the connection (with the expected gaps due to races when machines go down and the clustering software hasn't responded yet)

SO_REUSEPORT sounds like it extends this capability to multiple processes/threads inside one box, but with the re-balancing being done automatically by the kernel (with with very similar races when processes/threads go down and the kernel hasn't responded yet)

This is a very nice new feature to have available.