Consumer fintech, zero to 100k users
An EU-based consumer fintech building a mobile-first investing app for first-time retail investors. The mandate was simple: from blank slate to App Store and Play Store in under three months, with a real KYC funnel, real money movement, and infrastructure that wouldn't melt under launch traffic.
I owned the architecture end to end — React Native client, Node.js services, PostgreSQL with strict double-entry ledgering, and the integration layer to a regulated KYC/AML provider plus a brokerage settlement partner. Trading flows were built around an idempotent command bus so partial failures never corrupted user balances.
Post-launch the product crossed 100k monthly actives in seven months. P95 API latency held at 42 ms under launch-day load by aggressively caching the read paths and pushing all write contention into per-user queues.
Tech stack
The whole picture.
Top-level technologies. Specific packages and integrations are listed below.
Architecture
End to end.
- Next.js admin console for ops and compliance review
- Server Actions for KYC overrides and ledger inspection
- Bare React Native with native KYC SDK bridges (iOS/Android)
- Offline-first reads via Query persisted cache
- Biometric auth gate on every money-movement flow
- GraphQL gateway in front of 6 internal services
- Double-entry ledger in Postgres, no float math
- Per-user BullMQ queues to serialize trade commands
- Redis for read-heavy quote and portfolio caches
Libraries
Packages worth naming.
- Expo (bare workflow)RN shell + native modules
- TanStack Queryclient cache + optimistic updates
- Zustandsession and UI state
- Apollo ServerGraphQL gateway
- PrismaPostgres access layer
- Zodschema validation across boundaries
- BullMQper-user job queues
Integrations
External systems.
- Stripe Connectdeposits and payouts
- SumsubKYC / AML verification
- Plaidbank account linking
- Segmentproduct analytics pipeline
- Sentryclient and server error monitoring
- Datadoginfra and APM
Building something similar?
Tell me about the product. I'll come back with thoughts and a first shipping date.