Facebook is undergoing a massive design shift in capacity management and service placement to scale the efficiency of our datacenter resources. At the core of this shift is the Resource Allowance System (RAS) that continuously optimizes for the assignment of service demand to capacity supply. RAS ensures available capacity to all services despite challenges of random failures, correlated failures, maintenances, and overloading shared resources. Additionally, the quality of assignment determines how efficiently datacenter resources can be used which is critical at our scale. Please attend to the talk to learn about the challenges we are faced with, and the solution that we have already deployed for 80% of all servers at Facebook.