Online services are typically replicated on multiple servers in different datacenters, and have (at best) a loose association with specific end-hosts or locations. To meet the needs of these online services, we introduce SCAFFOLD---an architecture that provides flow-based anycast with (possibly moving) service instances. SCAFFOLD allows addresses to change as end-points move, in order to retain the scalability advantages of hierarchical addressing. Successive refinement in resolving service names limits the scope of churn to ensure scalability, while in-band signaling of new addresses supports seamless communication as end-points move.

We design, build, and evaluate a SCAFFOLD prototype that includes an end-host network stack (built as extensions to Linux and the BSD socket API) and a network infrastructure (built on top of OpenFlow and NOX). We demonstrate several applications, including a cluster of web servers, partitioned memcached servers, and migrating virtual machines, running on SCAFFOLD.