Load balancing for the witte kassa in restaurants

Every Belgian restaurant works with a witte kassa: the registered cash register system (GKS) that hospitality businesses are required to use. BMC makes the zwartedoos (Boîte Noire in French) that goes with it: a fiscal data module, or FDM. The FDM records every sale, so it can’t be erased.

The challenge

A large hospitality customer of BMC sometimes used up to 5 fiscal data modules, with several cash registers.

What we built

For that customer we wrote middleware in Rust that does the load balancing: the transactions of the cash registers are spread over the fiscal data modules. The middleware runs in the restaurant itself, so the load balancing happens inside the restaurant.

Why Rust

It had to be performant, and it had to run on very old hardware and possibly on different software.