RNG: Flat Datacenter Networks at Scale#

Ratul Mahajan – AWS

• Why: The most consequential physical DC topology talk of the meeting: Amazon claims the first production flat (non-tree) datacenter networks, solving the two problems — cabling and routing — that kept expander topologies academic for a decade. Directly in the PM's wheelhouse (topology, optics, cabling, routing).
• What: RNG (Random Resilient network Graphs) replaces fat trees with quasi-random graphs for most workloads at Amazon, now the default for new fabrics. Headline results from the deck: 69% fewer switches, 40% less power, 27% lower cost (slides also give 9–45% fewer switches depending on config), with application flows performing as well as or better than fat trees and graceful degradation under failures rather than the outsized impact trees suffer from small cuts.
• How: Three coupled inventions. ShuffleBox, a passive optical device that internally shuffles cables (e.g. 32×4×100G to 4×32×100G), giving random-graph connectivity with fat-tree-like cabling complexity. Spraypoint, a distributed routing protocol that exploits random-graph properties to find nearly all edge-disjoint paths via multi-level waypoints instead of shortest paths. Predictive models combining random-graph concentration properties with Spraypoint decorrelation, so oversubscription and path length are predictable at design time from topology parameters.
• Where applicable: AWS production (research 2022 → two experimental fabrics torn down 2024 → production 2025 → default). Not retrofittable — it assumes a custom passive optical shuffle and a new routing protocol — but it is the strongest evidence yet that expander/flat fabrics are operationally viable, and it should reshape any next-gen DC topology roadmap.