Darwin Hexagonal

Hexagonal Architecture (Ports & Adapters)

Core Principles

• Core domain isolation: Business logic MUST have zero import dependencies on infrastructure. No import redis, import kubernetes, import requests in domain modules.
• Ports: Interfaces defined BY the core domain (e.g., class EventStore(Protocol), class MetricsProvider(Protocol)). The core says what it needs; adapters provide it.
• Adapters: Implementations of ports for specific technologies (e.g., RedisEventStore, K8sMetricsProvider). Adapters import infrastructure libraries; the core never does.
• Dependency direction: Always inward. Adapters depend on ports. Core depends on nothing external.

When Reviewing Code

• Flag any business logic file that directly imports a database client, HTTP library, or cloud SDK
• Recommend extracting a port (interface) to decouple
• If a change modifies both a port interface and its adapter, flag it in the risk assessment

When Planning New Features

• Specify which port the new code enters through
• Specify which adapter will implement it
• If the port doesn't exist yet, design it as part of the plan
• Boundary crossings (modifying port + adapter) carry higher risk

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