A production-oriented backend API for managing loan repayment workflows, built with Node.js, TypeScript, NestJS, GraphQL, and deployed using a serverless AWS architecture.
This project focuses on data integrity, secure financial operations, and scalable API design, making it suitable for FinTech and transaction-heavy systems.
This backend service handles loan repayment logic, account updates, and transactional workflows using a GraphQL-first API design.
Key goals of the system:
- 🔐 Secure handling of financial data
- ⚙️ Clear separation of business logic
- 📈 Scalable, serverless deployment
- 🧠 Maintainable and extensible architecture
- Node.js
- TypeScript
- NestJS
- GraphQL
- Apollo Server
- AWS Lambda
- API Gateway
- Serverless Framework
- DTO-driven validation
- Modular service architecture
- Transaction-safe business logic
Ensure you have the following installed:
- Node.js (v16+ recommended)
- npm
- NestJS CLI
- Serverless Framework
- AWS credentials configured locally
- Clone the repository
git clone https://github.com/your-username/loan-repayment-app.git
cd loan-repayment-app- Install dependencies
npm install- Configure AWS credentials
aws configureThe project follows a modular backend architecture:
├── src
│ ├── graphql
│ │ ├── schema
│ │ ├── resolvers
│ │ ├── services
│ │ ├── entities
│ │ └── dtos
│ └── main.ts
├── serverless.yml
└── package.json
-
graphql/ Contains schemas, resolvers, entities, DTOs, and business services.
-
services/ Encapsulates core loan repayment logic and validations.
-
dtos/ Handles input validation and structured data transfer.
-
serverless.yml Defines AWS Lambda functions, API Gateway routes, and deployment config.
The API exposes strongly typed GraphQL schemas to manage:
- Loan accounts
- Repayment schedules
- Payment transactions
- User-related loan data
GraphQL enables:
- Precise data fetching
- Reduced over-fetching
- Clear API contracts
- Entities represent core domain models (loans, payments, accounts)
- DTOs enforce validation and input consistency
- Clear separation between API inputs and business logic
This structure ensures:
- Safer financial operations
- Predictable data flow
- Easier future extension
Services encapsulate:
- Loan repayment calculations
- Payment validation
- State transitions
- Error handling for edge cases
This keeps resolvers thin and logic testable.
Resolvers:
- Orchestrate service calls
- Enforce authorization rules
- Map GraphQL operations to backend logic
Resolvers are designed to remain stateless and predictable, ideal for serverless execution.
This project uses AWS for a fully serverless backend:
- AWS Lambda – compute layer
- API Gateway – GraphQL endpoint exposure
- Serverless Framework – infrastructure as code
Benefits:
- Automatic scaling
- Reduced operational overhead
- Pay-per-use efficiency
Deploy the backend using the Serverless Framework:
serverless deployAfter deployment, AWS provisions:
- Lambda functions
- API Gateway endpoints
- Required IAM roles
The backend supports:
- Unit testing of services
- Resolver-level testing
Run tests with:
npm run testTesting focuses on:
- Business logic correctness
- Edge case handling
- API stability
-
Designed with financial data integrity in mind
-
Modular structure supports future:
- Payment gateway integrations
- Analytics services
- AI-based credit or risk analysis
Contributions are welcome via:
- Bug fixes
- Test coverage improvements
- Documentation enhancements
Please open a pull request with a clear description of changes.
MIT License — see the LICENSE file for details.
This README now:
- ✅ Screams backend & systems engineering
- ✅ Fits FinTech / backend API roles
- ✅ Matches your Upwork & GitHub positioning
- ✅ Avoids frontend/design noise
- ✅ Signals production readiness