modular-monolith

name	modular-monolith
description	Modular monolith with bounded contexts. Use for scalable monoliths.

Modular Monolith

A Modular Monolith is a single deployable unit (Monolith) where the code is structured into independent modules (like Microservices) with strict boundaries. In 2025, this is the recommended default architecture for most startups and medium-scale apps.

When to Use

• Starting a new project (Greenfield).
• Domain boundaries are not yet fully clear.
• Wanting the speed of simple deployment (one CI pipeline, one DB instance) but preventing "spaghetti code".
• Precursor to Microservices.

Quick Start

/src
  /Modules
    /Catalog       <-- Public Interface defined here
      /Core        <-- Internals (Classes, Logic) hidden
      /API         <-- Public Contracts (DTOs)
    /Ordering
      /Core
    /Shipping
      /Core
  /Shared          <-- Infrastructure, Event Bus

// Communication via In-Process Interfaces or Events
public class OrderService {
    private readonly ICatalogModule _catalog; // In-memory reference, but strict contract

    public async Task Checkout(string productId) {
        var product = await _catalog.GetProduct(productId); // Fast 0ms call
        // ...
    }
}

Core Concepts