Back in 2017 Google shared details about Espresso which is their SDN solution for scaling up their routing. Saw this fascinating presentation from Google at SIGCOMM 2017. This blog post covers it in detail besides the talk. Key design principles for their routing platform Hierarchical control plane consisting of both global as well as local control. Global takes care of overall traffic flow, inputs coming from performance metric etc while local take care of failure of BGP sessions, port/device failure etc.