simplest-load-balancer

SLB (simplest-load-balancer) is a sessionless load balancer for UDP and solves problems inherent with using traditional (feature rich) load balancers for such traffic.

For simple, stateless UDP protocols there is no advantage in trying to maintain "affinity" (aka. "sessions") between clients and back-end instances. Traditional load balancers assume that affinity is helpful (it is for TCP and some stateful UDP protocols), and will try to route packets from a given client to a consistent back-end server. By contrast, SLB evenly (randomly) distributes packets all available back-ends. This results in uniform loading of backends, and improved robustness.

SLB features dynamic configuration with backends being added/refreshed, removed and configured (weights and port associations) dynamically via a UDP control plane. Switching backends during maintenance is nearly instantaneous (without sessions there is no need to wait to "drain" connections).

Inbound traffic is distributed based on port group assignments and "weights" which can be dynamically adjusted for each backend based on capacity, load, maintenance status or any other consideration.

When a more robust HA deployment with multiple SLBs is needed the communication between backends and SLB can be simplified by using a multicast group IP.