Self-Checkout Backend Platform

Backend-only, polyglot self-checkout platform with an event-driven orchestrator and domain-focused microservices.

Architecture Overview

• Orchestrator: NestJS with CQRS, event sourcing, sagas, and MongoDB persistence
• Product Service: Java and Spring Boot
• Cart Service: Ruby on Rails and Mongoid
• Payment Service: Go
• Inventory Service: C++
• Fraud Service: Rust
• Discount Engine: Python
• Audit Service: Kotlin and Spring Boot

Supporting infrastructure:

• Kafka and RabbitMQ
• PostgreSQL, MongoDB, Redis
• Consul
• Prometheus, Grafana, Jaeger
• Docker Compose, Kubernetes, Terraform

Repository Layout

.
├── docker-compose.yml
├── services/
│   ├── orchestrator/
│   ├── product-service/
│   ├── cart-service/
│   ├── payment-service/
│   ├── inventory-service/
│   ├── fraud-service/
│   ├── discount-engine/
│   └── audit-service/
├── shared/
│   └── protos/
├── k8s/
├── monitoring/
└── terraform/

Local Run

git clone <repository-url>
cd <repository-folder>
docker compose up -d

Main Endpoints

Service	URL
Orchestrator REST API	http://localhost:3000/api/v1/checkouts
Orchestrator Swagger	http://localhost:3000/api
Product Service	http://localhost:8080/api/v1/products
Cart Service	http://localhost:3001/api/v1/carts
Payment Service	http://localhost:8081/api/v1/payments
Inventory Service	http://localhost:8082/api/v1/inventory
Fraud Service	http://localhost:8083/api/v1/fraud/check
Discount Engine	http://localhost:5000/api/v1/discounts/calculate
Audit Service	http://localhost:8084/api/v1/audit
Grafana	http://localhost:3002
Prometheus	http://localhost:9090
Jaeger	http://localhost:16686
Consul	http://localhost:8500

Development Notes

• Backend-only repository
• Generated artifacts and local caches are excluded via the root .gitignore

Documentation

• shared/protos
• k8s
• terraform