Over-engineered ToDo app
A production-ready TypeScript/NestJS reference implementation of DDD, Hexagonal Architecture, CQRS, Event Sourcing, and Event-Driven Architecture.
What is Over-engineered ToDo app?
ddd-hexagonal-cqrs-es-eda is a complete, production-like reference implementation that demonstrates how to combine Domain-Driven Design, Hexagonal Architecture, CQRS, Event Sourcing, and Event-Driven Architecture in a TypeScript and NestJS application. It solves the problem of understanding how to practically apply these advanced patterns to build complex, maintainable software systems.
Backend and full-stack developers, software architects, and engineering teams who are designing or refactoring complex applications and want a real-world example of modern architectural patterns.
Developers choose this project because it provides a fully working, well-documented example that bridges the gap between theory and practice, showcasing how these patterns integrate in a single codebase with production-grade tooling like observability and testing.
Overview
Complete working example of using Domain Driven Design (DDD), Hexagonal Architecture, CQRS, Event Sourcing (ES), Event Driven Architecture (EDA), Behaviour Driven Development (BDD) using TypeScript and NestJS. Like what you see? Don't forget to star! ⭐ ^^^
Use Cases
Best For
- Learning how to implement Hexagonal Architecture with Ports and Adapters
- Understanding Domain-Driven Design tactical patterns in TypeScript
- Building event-driven systems with CQRS and Event Sourcing
- Creating modular applications that can switch between monolith and microservices
- Studying observability integration (tracing, logging, metrics) in a complex app
- Reference for structuring large NestJS projects with bounded contexts
Not Ideal For
- Projects needing rapid MVP development without advanced architectural overhead
- Teams lacking Docker and distributed systems expertise for complex infrastructure setup
- Applications with simple CRUD operations where event sourcing and CQRS add unnecessary complexity
- Environments with limited computational resources, as it requires multiple running services (NATS, databases, observability tools)
Pros & Cons
Pros
Demonstrates how Hexagonal Architecture, DDD, CQRS, and Event-Driven Architecture work together in a single codebase, with clear module separation and event storming documentation from the README.
Includes observability with Jaeger and Prometheus, behavior-driven tests, and flexible deployment options, making it a near-production-ready reference for complex systems.
Uses bounded contexts and ports/adapters to decouple the domain layer, enabling easy switching between modular monolith and microservices configurations as described in the technical features.
Provides a working Todo app with detailed explanations, theoretical reviews, and event storming maps, effectively bridging the gap between software architecture theory and implementation.
Cons
Requires Docker, multiple services (e.g., NATS, PostgreSQL, MongoDB), and has a steep learning curve, which the README acknowledges can be challenging for quick starts.
Described as an 'over-engineered ToDo app' in the README, making it unsuitable for projects where architectural purity outweighs practical needs, leading to unnecessary boilerplate.
Includes deprecated features like gRPC query caching, which may confuse users and require updates or workarounds for modern deployments, as noted in the technologies section.
Frequently Asked Questions
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