Meta has open-sourced Rebalancer, an assignment solver that the company says has been in production for more than nine years. The library, written in C++ with Python bindings, is now available as a package that can be installed via pip.
Rebalancer is designed to place shards, servers, and traffic across infrastructure. According to Meta, it processes roughly 40 million assignment problems each day. The solver can run in two modes: local search for speed, or mixed-integer programming (MIP) with external solvers such as Gurobi, FICO Xpress, and HiGHS.
By open-sourcing the tool, Meta is giving other organizations a way to reuse a battle-tested component of its infrastructure. The announcement does not include benchmarks beyond the daily problem count, so performance in other environments will depend on the chosen solver and problem structure.