JCON ONLINE 2022

Payment is part of everyday life. Whatever we buy, we need to pay for, right? For consumers this seems simple: only engineers understand the deep complexities inside payments – and consumers’ low tolerance for error. With every new feature added to a payments platform, the potential risks increase. After launching the world’s first pure-play grocery retailing website 20 years ago, we’ve developed the Ocado Smart Platform (OSP), our end-to-end online grocery fulfilment solution, adopted by 11 of the world’s most forward-thinking retailers. How did we develop our payments solution to rapidly scale, while avoiding pitfalls like highly coupled code, low cohesion modules, transactional script-based layers, anaemic models, or fragile tests? In this talk, we’ll share: 1) How we are restructuring our core payment monolith into decoupled modules - Modular Monolith - using Hexagonal Architecture driven by UseCase semantics - to improve our system’s modularity, allow for fast parallel work, and seamless evolution of the codebase. 2) Our Behaviour Driven Development based testing strategy, which allows us to freely refactor our code without tests breaking due to mocking side effects. 3) Finally, we'll share how we leverage Domain Events to increase our system's modularity.