Understanding Hexagonal Architecture

January 18, 2025 | Architectures

Hexagonal Architecture, also known as the Ports and Adapters pattern, is a software design principle that aims to create maintainable and flexible applications by decoupling business logic from external systems. This architecture was introduced by Alistair Cockburn and is widely used in modern software development.

Core Concepts

1. Business Logic (Domain Layer)

At the heart of Hexagonal Architecture lies the business logic, which represents the core functionality of the application. It is independent of frameworks, databases, or external services.

2. Ports (Interfaces)

Ports define how the core domain interacts with the outside world. These are abstractions that act as entry points or communication channels.

3. Adapters (Implementations)

Adapters are responsible for implementing the ports. They act as bridges between the application’s core logic and external components such as databases, APIs, or user interfaces.

Structure of Hexagonal Architecture

The architecture is commonly visualized as a hexagon, with:

• The core domain at the center.
• Ports forming the edges of the hexagon.
• Adapters connecting to ports to interact with external systems.

Benefits of Hexagonal Architecture

✅ Separation of Concerns - Keeps business logic isolated from infrastructure details.

✅ Flexibility - Allows easy replacement of external systems like databases or APIs.

✅ Testability - Simplifies unit testing by using interfaces for dependencies.

✅ Maintainability - Encourages clean and modular code.

Example in JavaScript/TypeScript

Here’s a simple implementation using TypeScript:

// Defining a Port (Interface)
interface PaymentProcessor {
  processPayment(amount: number): boolean;
}

// Implementing an Adapter (External Service)
class PayPalAdapter implements PaymentProcessor {
  processPayment(amount: number): boolean {
    console.log(`Processing payment of $${amount} via PayPal.`);
    return true;
  }
}

// Core Business Logic
class CheckoutService {
  constructor(private paymentProcessor: PaymentProcessor) {}

  checkout(amount: number) {
    if (this.paymentProcessor.processPayment(amount)) {
      console.log("Payment successful!");
    } else {
      console.log("Payment failed.");
    }
  }
}

// Using the Adapter
const paymentAdapter = new PayPalAdapter();
const checkout = new CheckoutService(paymentAdapter);
checkout.checkout(100);