Remote · Full-Time · Senior (5+ Years)

We're looking for a Senior Ruby on Rails Engineer to join our team as a technical anchor for CardCorp, our primary production platform. This is a role for an autonomous "thinking" developer — someone who values deep research over quick fixes and understands that in fintech, correctness sets the ceiling, not velocity. You'll be responsible for maintaining the architectural integrity of a data-heavy ecosystem, ensuring that complex calculations and high-volume ingestions remain accurate to the cent.

The Engineering Challenge: Our environment is not a standard CRUD application. You'll be managing high-scale ingestion pipelines that process hundreds of thousands of records across interconnected CSV imports and multi-source data feeds. You'll be building and refactoring multi-tier calculation engines for fees, revenues, and FX, where Float is never an option and rounding logic must be deterministic. And you'll be navigating complex, callback-driven Sidekiq worker chains where idempotency and race-condition management are daily requirements, not edge cases.

Technical Stack: On the backend, we run Ruby 3.2 on Rails 8, with PostgreSQL as our database (expert usage expected: JSONB, CTEs, window functions, and custom indexing). Background processing is handled by Sidekiq 6+ (Cron, Unique-Jobs, Status) with Redis, and our architectural patterns lean on Dry-rb for validations and types, service-object architecture, and Pundit for multi-tenant authorization.

CardCorp, our primary product, runs on a modern Hotwire stack (Turbo Frames, Turbo Streams, StimulusJS) with Tailwind CSS and Chart.js. BillPro, our secondary product, is a Rails JSON API supporting a Vue.js SPA.

On the infrastructure side, we deploy via Docker and Dokku with GitHub Actions, and use Sentry for observability alongside request-ID correlation and custom logging for financial audits.

What We Expect from You: You should be fluent in all of the following from day one. Advanced PostgreSQL — you don't just write queries, you profile them; you understand lock contention, isolation levels, and how to design zero-downtime migrations on tables with millions of rows. Data pipeline design — you know when to stream data, when to batch, and how to avoid memory exhaustion when cross-referencing massive datasets in-memory. Sidekiq mastery — you can reason about long worker chains and eventual consistency, and you treat idempotency as a design requirement, not an afterthought. Architectural discipline — you have experience leading service-layer abstractions that are easy to test and deterministic in behaviour, and you know when a "concern" is just a band-aid for a missing object. Modern Rails UI — you're proficient with Hotwire and know how to build reactive interfaces without the overhead of a heavy SPA framework, but you're comfortable enough with Vue.js to contribute to our API-driven products. And serious professionalism — you take ownership of your tasks, research industry standards before implementing a solution, and stay disciplined about code quality and testing.

Nice to Have: Prior experience in fintech, PSP, or payment processing. Strong opinions on clean code and "boring" technology that scales.

Rule number one: Apply through the link - https://apply.unicorn-hunt.com/apply/cardcorp