Stateless Datacenter Load-balancing with Beamer

Datacenter load balancers (or muxes) steer traffic destined to a given service across a dynamic set of backend machines. To ensure consistent load balancing decisions when backends come or leave, existing solutions make a load balancing decision per connection and then store it as per-connection state to be used for future packets. While simple to implement, per-connection state is brittle: SYN-flood attacks easily fill state memory, preventing muxes from keeping state for good connections. We present Beamer, a datacenter load-balancer that is designed to ensure stateless mux operation. The key idea is to leverage the connection state already stored in backend servers to ensure that connections are never dropped under churn: when a server receives a mid-connection packet for which it doesn't have state, it forwards it to another server that should have state for the packet. Stateless load balancing brings many benefits: our software implementation of Beamer is twice faster than Google's Maglev, the state of the art software load balancer, and can process 40Gbps of HTTP uplink traffic on 7 cores. Beamer is simple to deploy both in software and in hardware as our P4 implementation shows. Finally, Beamer allows arbitrary scale-out and scale-in events without dropping any connections.