Addressing Technical Debt in Messaging Systems with Extensible State Machines

The presentation outlines the challenges encountered with an old, intractable codebase for a messaging system, Mongos, based on XMPP. The system faced significant technical debt due to incremental improvements and extensions over a decade. To address this, the speakers developed a new, extensible core using OTP’s gen_statem behavior, allowing for modular extensions without modifying core code. This approach not only cleaned the code but also improved system performance. They shared practical examples of refactoring such as configuration and API rework, emphasizing modularity and loose coupling. The session concluded with a Q&A highlighting the benefits of disabling unnecessary protocols like presence to improve performance.