Python Subscription Platform

Production-grade backend service for managing subscriptions, billing, and order lifecycles in a SaaS-like environment.

Overview

This project simulates a real-world backend responsible for subscription management, billing workflows, and access control.
The focus is on clean architecture, business-oriented modeling, and explicit trade-offs, rather than CRUD-only APIs.

Core Features

• User and account management
• Subscription plans and lifecycle handling
• Billing and payment workflows (mocked external provider)
• Role-based access control (RBAC)
• Webhook ingestion with idempotency
• Input validation and structured error handling

Architecture

The system follows a layered architecture inspired by DDD, without overengineering:

• domain → business rules and entities
• application → use cases and orchestration
• infrastructure → database, auth, and web frameworks

This separation allows:

• Business logic to remain framework-agnostic
• Easier testing of domain rules
• Clear ownership of responsibilities

Tech Stack

• Python
• FastAPI
• PostgreSQL
• SQLAlchemy
• JWT / OAuth2
• Pytest

Design Decisions

• Monolithic architecture: chosen for simplicity and operational clarity
• FastAPI: async support and strong OpenAPI integration
• PostgreSQL: transactional consistency and mature ecosystem
• Explicit use cases instead of fat controllers

Testing Strategy

• Unit tests for domain logic
• Focus on business rules rather than framework behavior

Non-Goals

• Microservices architecture
• Frontend application
• Real payment provider integration

Future Improvements

• Async task processing
• Rate limiting
• Audit logs