In real-world SaaS systems, the hard part is not writing CRUD endpoints.
The real challenge is getting architecture, security, multi-tenancy, and scalability right from day one.
That’s why I built Nexus API — a production-grade NestJS backend foundation designed for serious SaaS products.
Repository:
👉 https://github.com/MertcanMert/nexus-api
🎯 Purpose of the Project
Nexus API is not a demo backend and not a tutorial project.
It is designed to solve real problems commonly ignored in early-stage backends:
- Multi-tenant architecture
- Secure authentication and authorization
- Audit logging and traceability
- Background jobs and async processing
- Modular, testable codebase
- Deployment-ready infrastructure
🧱 Architecture Overview
Modular, Layered Structure
src/
├─ common/ → guards, interceptors, decorators, config
├─ infrastructure/ → prisma, mail, storage, background jobs
├─ modules/ → auth, user, health
└─ main.ts
Key principles:
- Clear separation between business logic and infrastructure
- Cross-cutting concerns handled via guards and interceptors
- Feature-based module organization
- Framework kept out of core domain logic as much as possible
🔐 Authentication & Authorization
- JWT + Refresh Token strategy
- Role-Based Access Control (RBAC)
- Policy-based authorization using an ability factory pattern
- Ownership guards for resource-level access control
Goal:
Prevent “logged-in but can access everything” systems.
🧬 Real Multi-Tenancy
Every critical action answers:
- Who did it?
- On which tenant?
- When?
- On which resource?
Audit logging is:
- Interceptor-driven
- Processed asynchronously via background jobs
- Non-blocking for API performance
⚙️ Background Jobs & Async Processing
Handled asynchronously:
- Email delivery
- Audit log processing
- Long-running or non-critical tasks
🧪 Testing Strategy
Testing is not cosmetic.
- Unit tests for services, repositories, guards
- End-to-end tests for authentication and tenancy
- Tests cover real scenarios, not just happy paths
📦 DevOps & Deployment Readiness
Out of the box:
- Docker & docker-compose setup
- Environment-based configuration
- Production build separation
- Prisma migrations fully integrated
This backend is ready to be deployed, not just run locally.
📚 Documentation Matters
The repository includes documentation for:
Architecture decisions (ADR)
- Security hardening
- Performance considerations
- API standards
- Roadmap planning
Because in production systems:
Documentation is part of the product.
Who Is This For?
- Backend engineers building SaaS platforms
- Developers using NestJS in real production systems
- Freelancers needing a solid backend foundation
- Engineers who want to avoid rewriting the same infrastructure again
Final Thoughts
Nexus API is:
- Not a framework showcase
- Not tutorial code
- Not a copy–paste boilerplate
It is a backend foundation that can confidently answer this question:
“Can this system go to production tomorrow?”
Repository:
👉 https://github.com/MertcanMert/nexus-api
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