[mcpherrinm]

It's documented as:

> For UDP traffic, the load balancer selects a target using a flow hash algorithm based on the protocol, source IP address, source port, destination IP address, and destination port. A UDP flow has the same source and destination, so it is consistently routed to a single target throughout its lifetime. Different UDP flows have different sources, so they can be routed to different targets.

From the NLB docs at https://docs.aws.amazon.com/elasticloadbalancing/latest/netw...