Overview

This project implements a transaction processing system with asynchronous antifraud validation using an event-driven microservices architecture.

Every transaction is:

• Created with an initial pending status
• Sent to an antifraud service via Kafka
• Validated asynchronously
• Updated to approved or rejected

The solution prioritizes decoupling, scalability, and eventual consistency, following real-world financial system patterns.

Architecture

Grafic

Design Decisions

Why Kafka?

• Decouples transaction creation from antifraud validation
• Allows horizontal scaling of antifraud workers
• Enables eventual consistency
• Prevents tight coupling between services

Why separate Antifraud Service?

• Each microservice owns a single responsibility
• Antifraud does not access the transaction database
• Communication happens only through events

Why asynchronous validation?

• Transactions are not blocked by antifraud latency
• System remains responsive under high load
• Mirrors real banking / fintech flows

Services

■ Transaction Service

• REST API (NestJS)

• PostgreSQL persistence (Prisma)

• Kafka producer & consumer

• Manages transaction lifecycle

■ Antifraud Service

• Kafka consumer & producer only

• No HTTP server

• No database

• Applies antifraud rule:

  » value > 1000 → rejected

  » otherwise → approved

API Reference

Create Transaction

  POST /transactions

Parameter	Type	Description
api_keyaccountExternalIdDebit	string	Required.
accountExternalIdCredit	string	Required.
tranferTypeId	int	Required. 1 for Yapeo/2 for Pago de Servicios/3 for Recarga de Celular
value	float	Required.

Get Transaction

  GET /transactions/${transactionExternalId}

Parameter	Type	Description
transactionExternalId	string	Required.

Running Tests

Unit Tests

• Business rules validation
• Initial transaction status
• Kafka producer mocked

E2E Tests

• POST /transactions
• GET /transactions/:id
• Prisma and Kafka mocked

To run tests, run the following command

  npm run test

Deployment

Requirements

• Docker

• Docker Compose

Run everything:

  docker compose up --build

This starts:

• PostgreSQL
• Zookeeper
• Kafka
• Transaction Service (port 3000)
• Antifraud Service (worker)

Environment Variables

To run this project, you will need to add the following environment variables to your .env file

DATABASE_URL="postgresql://postgres:postgres@postgres:5432/postgres"

Feedback

If you have any feedback, please reach out to us at andersson26012000@gmail.com

Authors

• Piero Andersson Sanchez Bazan (BackEnd Developer)