architecture-patterns

1# Architecture Patterns
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3Master proven backend architecture patterns including Clean Architecture, Hexagonal Architecture, and Domain-Driven Design to build maintainable, testable, and scalable systems.
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5**Given:** a service boundary or module to architect.
6**Produces:** layered structure with clear dependency rules, interface definitions, and test boundaries.
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8## When to Use This Skill
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10- Designing new backend services or microservices from scratch
11- Refactoring monolithic applications where business logic is entangled with ORM models or HTTP concerns
12- Establishing bounded contexts before splitting a system into services
13- Debugging dependency cycles where infrastructure code bleeds into the domain layer
14- Creating testable codebases where use-case tests do not require a running database
15- Implementing domain-driven design tactical patterns (aggregates, value objects, domain events)
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17## Core Concepts
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19### 1. Clean Architecture (Uncle Bob)
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21**Layers (dependency flows inward):**
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23- **Entities**: Core business models, no framework imports
24- **Use Cases**: Application business rules, orchestrate entities
25- **Interface Adapters**: Controllers, presenters, gateways — translate between use cases and external formats
26- **Frameworks & Drivers**: UI, database, external services — all at the outermost ring
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28**Key Principles:**
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30- Dependencies point inward only; inner layers know nothing about outer layers
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