Building Scalable REST APIs with NestJS and PostgreSQL
How I architected a production API serving 500K+ requests/day with proper error handling, validation, and documentation.
When our team needed to rebuild a legacy Express API that was struggling under load, we chose NestJS for its TypeScript-first approach and modular architecture. Here's how we built an API that now handles 500K+ requests daily.
Why NestJS Over Express?
After evaluating several frameworks, NestJS stood out for several reasons:
- **TypeScript by Default**: No configuration needed, full type safety out of the box
- **Dependency Injection**: Makes testing and modularity much easier
- **Opinionated Structure**: New team members can onboard quickly
- **Built-in Validation**: Using class-validator and class-transformer
Architecture Overview
We structured our API using a clean architecture approach with modules, controllers, services, and repositories. Each module encapsulates a specific domain like users, orders, or products.
Key Patterns We Used
Repository Pattern
Abstracting database operations made testing much easier and allowed us to swap PostgreSQL for in-memory storage during tests.
Global Exception Filter
Consistent error responses across all endpoints, with proper logging and error tracking.
Request Validation
Using DTOs with class-validator ensured invalid data never reached our business logic.
Performance Optimizations
- Connection pooling with pg-pool for efficient database connections
- Redis caching for frequently accessed data
- Database query optimization with proper indexing
- Response compression with gzip
- Rate limiting to prevent abuse
Results
After migration: - Response times decreased by 60% - Error rates dropped by 85% - Developer productivity increased significantly - Onboarding time for new developers reduced from weeks to days
The modular architecture also made it easy to add new features without affecting existing functionality.
David Sampson
Senior Full Stack Engineer