Building Prometheus: How Backend Aggregation Enables Gigawatt-Scale AI Clusters

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This post details the crucial role of Backend Aggregation (BAG) in building gigawatt-scale AI clusters like Prometheus. It explains how BAG interconnects thousands of GPUs across multiple data centers and regions by acting as a centralized Ethernet-based super spine network layer. The post elaborates on BAG's implementation, including its connection to different network fabrics (DSF and NSF), inter-BAG topologies (planar and spread), hardware and routing strategies (Jericho3 ASICs, eBGP with UCMP), and design considerations for resilience and long cable distances.