Full Stack Engineer For an Leagcy Investment Platform

``` Senior Full-Stack Engineer — Next.js + Fastify + PostgreSQL Investment Platform ``` Alternatives if you want a different hook: ``` Full-Stack TypeScript Engineer — Fintech Investment Platform (Node, Next.js, AWS) Node + Next.js Engineer for Equity-Crowdfunding Platform Build (3 months, AWS) ``` --- ## Job description — paste from here ``` We are rebuilding an alternative-investment and equity-crowdfunding platform from scratch and are looking for a senior full-stack engineer to join a small team for the build. Three-month engagement, six two-week sprints plus a cut-over week, with the possibility of continuing afterwards. This is a money-handling platform. Correctness, auditability and authorisation matter more here than shipping fast, and the codebase is held to that standard. WHAT WE ARE BUILDING A platform that presents investment opportunities to the public, takes an investor from sign-up through KYC to a signed and paid investment, gives investors a dashboard to track what they own, and gives an internal team a full back-office — including a CMS they edit themselves with no developer involved. Twelve modules in total: identity and access, projects, fundraising rounds, investments, contracts and e-signature, payments, investor portal, CMS, notifications, support, affiliates, and finance reporting. There is a legacy system whose data and files migrate across without losses and without duplicates. That migration is part of the build. ARCHITECTURE AND STACK • Domain-oriented modular monolith — one deployable, twelve modules with hard internal boundaries. Each module owns its tables and is reached only through what it publishes. • Front-end: Next.js 14 App Router, React 18, TypeScript, Tailwind CSS • Back-end: Node.js 20, Fastify, TypeScript, Prisma, Zod • Data: PostgreSQL 16 on RDS, ElastiCache for Valkey, S3 with pre-signed URLs • Async: Amazon SQS with dead-letter queues and a dedicated worker instance — every slow job (e-mail, SMS, contract generation, e-signature, reports) runs off the request path • Infra: AWS (EC2, Lightsail, RDS, SQS, ElastiCache, S3, CloudWatch), Docker, GitHub Actions, PM2. Trunk-based development, one required review per merge. • Testing: Vitest, Testcontainers, Supertest, Playwright, k6 WHAT YOU WOULD OWN One of three tracks, depending on your strengths: • Transactional core — investments, contracts, payments: the state machine, allocation arithmetic, idempotency, the e-signature integration, financial exports • Front-end and experience — public site, investor portal, CMS front-end, design system, SSR and SEO, accessibility • Platform and data — identity and access control, notifications, the worker, and the legacy data migration Everyone works across the stack and reviews outside their own track. WHAT WE NEED FROM YOU • Strong TypeScript on both ends — types that make illegal states unrepresentable • Production Node.js on the server: Fastify or Express, schema-first validation • React and Next.js App Router, including SSR and where the client/server boundary falls • Real PostgreSQL skill: transactions, isolation levels, indexes, and correct decimal arithmetic for money. You know why a float is wrong here without being told. • Queue-based async work you have actually implemented: retries, back-off, dead-lettering, idempotency • You write tests as part of the work — unit, integration against real infrastructure, and API contract tests • Comfortable reading and reasoning about someone else's legacy schema • Small reviewable pull requests and proper code review NICE TO HAVE Prisma, Zod, Tailwind, AWS at the level above, Playwright or k6, previous fintech or payments work, ETL/data-migration experience with reconciliation, Docker, GitHub Actions. HOW WE WORK Agile, two-week sprints, English, daily async updates with a short live standup. Definition of Done includes tests, the authorisation matrix for any new route, an updated OpenAPI spec and a staging demo. We do not count hours against a stopwatch; we care that the sprint commitment is real and that you flag early when it is not. TO APPLY Skip the template cover letter. Tell us about one system you built where correctness mattered more than speed, and what you did to guarantee it. Include a link to code we can read if you have one. ``` ## Paste to here --- ## Screening questions Upwork allows up to five. These are ordered by how fast they disqualify. 1. Describe a system you built where getting it wrong meant wrong money or lost data. What specifically did you do to make it correct? 2. How do you make a background job safe to run twice? Give a concrete example from something you shipped. 3. How do you store and calculate monetary amounts in PostgreSQL, and why? 4. Have you migrated data from a legacy production database into a new schema? How did you verify nothing was lost or duplicated? 5. Which of the three tracks (transactional core / front-end / platform and data) fits you best, and why? --- ## Skills tags Primary: TypeScript · Node.js · Next.js · React · PostgreSQL · Fastify · Prisma · AWS Secondary: REST API · Amazon SQS · Docker · Tailwind CSS · Zod · Playwright · Full-Stack Development --- ## Suggested form settings | Field | Suggestion | |---|---| | Category | Web, Mobile & Software Dev → Full Stack Development | | Scope | Large · 3 to 6 months · Expert | | Contract | Hourly, 30–40 hrs/week, with a weekly cap — a fixed-price contract does not fit a scope that is discovered sprint by sprint | | Contract-to-hire | Optional but worth switching on | | Location | Set your own preference; the post assumes an overlap window rather than a timezone | | Talent quality | Rising Talent or Top Rated, 90%+ job success | | Rate range | Set in the form, not in the post — the body deliberately carries no numbers |