Flier: Flow-level congestion-aware routing for direct-connect data centers.

Various topologies have been proposed in the context of high-performance computing and data center networking. Direct-connect topologies generally offer large capacity with high path diversity and are highly cost effective for general data center traffic patterns. However, the lack of simple yet efficient load balancing techniques for direct-connect fabrics has hindered these networks from gaining traction in data centers. This paper presents the design, implementation, and evaluation of Flicr, a light-weight host-based load balancing mechanism for direct-connect data centers. Flicr dynamically reroutes traffic through minimal and non-minimal routes to avoid congesting the fabric. This enables Flicr to efficiently minimize networking resource consumption while exploiting high path diversity in direct-connect fabrics to balance the network and gracefully handle link failures. Flicr requires only a simple kernel modification and is readily deployable in commodity data centers today. Our evaluations show that Flicr consistently outperforms other state-of-the-art load balancing designs, achieving 25–60% lower average flow completion time compared to adaptive routing. Flicr is also more robust against link failures and has 5–8 χ better performance relative to other schemes in the presence of link failures.