Background When the client reached out to us, the product was already live in production — a B2B fintech platform that was rapidly gaining users. However, the code remained a legacy of the MVP stage: modules written in a rush, chaotic integrations with external services, and technical debt that weighed heavily on the team. The client's developers were working flat out, while bugs and integration failures had become a normal part of the day.
Solution We introduced a Middle+ Java Backend engineer who became part of the team from day one. They quickly got up to speed with the architecture and started with the most problematic area — the commission calculation module. The logic there changed constantly, with little to no real architecture in place. The engineer built a testable structure, baked in extensibility for future scenarios, and made the service functional and understandable.
Deliverables
Commission module redesign: A clean, testable, and extensible architecture was put in place, allowing business logic to change without breaking everything around it.
API decoupling & optimization: The public API was separated from internal interfaces. Throttling was added for heavy requests, and part of the logic was moved to a dedicated microservice.
Kafka overhaul: Previously used without a clear system, topics were reorganised, consumer services were rewritten to be idempotent, and DLQ (Dead Letter Queue) topics were added to capture and isolate problematic messages.
CI/CD improvements: Static code analysis was added. Tests were sped up by running them in parallel. QA and analysts could validate changes faster.
Beyond the code The engineer didn't just write code — they became embedded in the product life cycle. They investigated production logs without being asked, communicated with the team as an equal, and proposed solutions even when the client was still trying to articulate the problem.
Outcome & Impact Within a few weeks, the client experienced their first "quiet" sprints — no critical failures, tasks completed on time, and a normal, sustainable pace of work. The team was able to switch from putting out fires to moving the product forward.