Decomposition Patterns — Deep Dive

graph TD
    subgraph Business Capabilities
        A[Order Management]
        B[Inventory Management]
        C[Customer Management]
        D[Payment Processing]
        E[Shipping]
    end
    A --> AS[Order Service]
    B --> BS[Inventory Service]
    C --> CS[Customer Service]
    D --> DS[Payment Service]
    E --> ES[Shipping Service]

graph TD
    subgraph Problem Space
        A[Core: Pricing Algorithm]
        B[Core: Recommendation Engine]
        C[Supporting: Order Processing]
        D[Supporting: Inventory]
        E[Generic: Authentication]
        F[Generic: Notifications]
    end
    A --> AS[Pricing Service]
    B --> BS[Recommendation Service]
    C --> CS[Order Service]
    D --> DS[Inventory Service]
    E --> ES[Auth0 - SaaS]
    F --> FS[SendGrid - SaaS]

graph TD
    subgraph Phase 1
        C1[Client] --> F1[Facade]
        F1 -->|100%| M1[Monolith]
    end

graph TD
    subgraph Phase 2
        C2[Client] --> F2[Facade]
        F2 -->|Old routes| M2[Monolith]
        F2 -->|New routes| S2[New Service]
    end

graph TD
    subgraph Phase 3 - Final
        C3[Client] --> F3[API Gateway]
        F3 --> S3A[Service A]
        F3 --> S3B[Service B]
        F3 --> S3C[Service C]
    end

# API Gateway configuration (Kong/Envoy)
routes:
  - path: /api/orders/*
    destination: order-service  # New service
  - path: /api/inventory/*
    destination: inventory-service  # New service
  - path: /*
    destination: monolith  # Everything else

graph TD
    subgraph Step 1 - Before
        A1[Client Code]
        B1[Old Implementation]
        A1 --> B1
    end

graph TD
    subgraph Step 2 - Introduce Abstraction
        A2[Client Code]
        I2[Interface/Abstraction]
        B2[Old Implementation]
        A2 --> I2
        I2 --> B2
    end

graph TD
    subgraph Step 3 - Parallel Implementations
        A3[Client Code]
        I3[Interface]
        B3[Old Implementation]
        C3[New Implementation]
        A3 --> I3
        I3 --> B3
        I3 -.->|Feature flag| C3
    end

graph TD
    subgraph Step 4 - Switch
        A4[Client Code]
        I4[Interface]
        C4[New Implementation]
        A4 --> I4
        I4 --> C4
    end

graph TD
    A[UI Service]
    B[Business Logic Service]
    C[Data Access Service]
    A --> B --> C

graph TD
    A[User Service]
    B[Order Service]
    C[OrderLine Service]
    D[Product Service]
    B --> C

graph TD
    A[New Feature] --> B{Clear bounded context?}
    B -->|Yes| C{Team available?}
    B -->|No| D[Keep in existing service]
    C -->|Yes| E[New microservice]
    C -->|No| F[Module in existing service]
    F --> G{Growing complex?}
    G -->|Yes| H[Extract later]
    G -->|No| D