Open-sourcing Rebalancer for solving resource allocation problems

Meta has open-sourced Rebalancer, a framework designed to solve complex resource allocation and assignment problems across large-scale infrastructure. The library has been used internally at Meta for over nine years to manage hardware placement, service allocation, task scheduling, and global traffic routing.

Solving resource allocation challenges

Assignment problems involve matching a set of objects to a set of bins while optimizing specific objectives and respecting constraints. At Meta, this includes positioning server racks in datacenters to handle power and cooling limitations, assigning servers to services to maximize fault tolerance, and routing user traffic to geographically distributed datacenters.

Developing a reusable framework for these tasks presents major challenges in usability and scalability. Practitioners often struggle to translate real-life policies into formal mathematical formulas, while complex models can be difficult for standard solvers to handle efficiently. Rebalancer addresses this by cleanly separating how a problem is specified from how it is solved.

Specification and solvers

Rebalancer provides a high-level specification language that uses modeling constructs such as dimensions, partitions, scopes, and utilization. Users describe problems using predefined recipes known as specs, which automatically generate the underlying mathematical formulas. Once specified, the framework translates the problem into an expression graph.