Financial software carries unique constraints that most development teams aren't prepared for. A bug in a social media app is annoying. A bug in a payment system can violate regulations and cost millions. Here's what we've learned from building fintech products across Latin America and the US.
Compliance Frameworks You'll Encounter
- PCI-DSS — Required if you touch credit card data. 12 requirements covering network security, encryption, access control, and monitoring.
- SOC 2 — Trust Service Criteria covering security, availability, processing integrity, confidentiality, and privacy. Often required by enterprise clients.
- KYC/AML — Know Your Customer and Anti-Money Laundering. Identity verification, transaction monitoring, suspicious activity reporting.
- GDPR/CCPA — Data protection regulations affecting how you store and process personal financial data.
Architecture Patterns for Fintech
Immutable Audit Logs
Every state change must be logged immutably. Use append-only tables or event sourcing. Regulators will ask "what happened to account X on date Y" — you must be able to answer with certainty.
Encryption at Every Layer
- In transit: TLS 1.3 everywhere, including internal service-to-service
- At rest: AES-256 for all PII and financial data
- Application-level: Encrypt sensitive fields before database storage
- Key management: AWS KMS or HashiCorp Vault — never store keys alongside data
Idempotent Transactions
Network failures happen. If a payment request is retried, it must not charge twice. Every transaction endpoint needs an idempotency key that prevents duplicate processing.
Real-Time Fraud Detection
Build a rules engine that evaluates transactions in real-time: velocity checks, geographic anomalies, amount thresholds, device fingerprinting. Start with rules, layer on ML as your data grows.
Testing Financial Software
Standard unit and integration tests aren't enough. Fintech requires:
- Property-based testing — Verify that money never appears or disappears in the system
- Chaos engineering — What happens when the payment provider is down? When the database failovers?
- Penetration testing — Annual third-party pentests are often a compliance requirement
- Load testing — Financial systems must handle 10x normal load during peak periods
Building a fintech product? Our team has the compliance and engineering expertise to get it right.
