Balancing on the Edge: Transport Affinity without Network State

Content delivery networks and edge peering facilities have unique operating constraints which require novel approaches to load balancing. Contrary to traditional, centralized datacenter networks, physical space is heavily constrained. This limitation drives both the need for greater efficiency, maximizing the ability to absorb denial of service attacks and flash crowds at the edge, and seamless failover, minimizing the impact of maintenance on service availability. This paper introduces Faild, a distributed load balancer which runs on commodity hardware and achieves graceful failover without relying on network state, providing a cost-effective and scalable alternative to existing proposals. Faild allows any individual component of the edge network to be removed from service without breaking existing connections, a property which has proved instrumental in sustaining the growth of a large global edge network over the past four years. As a consequence of this operational experience, we further document unexpected protocol interactions stemming from misconfigured devices in the wild which have significant ramifications for transport protocol design.