Integration Patterns — Deep Dive

graph TD
    M[Mobile] --> GW[API Gateway]
    W[Web] --> GW
    P[Partner] --> GW
    GW --> O[Order Service]
    GW --> U[User Service]
    GW --> PAY[Payment Service]

services:
  - name: order-service
    url: http://order-service:8080
    routes:
      - name: orders-route
        paths:
          - /api/orders

  - name: user-service
    url: http://user-service:8080
    routes:
      - name: users-route
        paths:
          - /api/users

graph TD
    M[Mobile App] --> MBFF[Mobile BFF]
    W[Web App] --> WBFF[Web BFF]
    P[Partner API] --> PBFF[Partner BFF]
    MBFF --> O[Order Service]
    WBFF --> O
    PBFF --> O
    MBFF --> U[User Service]
    WBFF --> U

sequenceDiagram
    participant C as Client Service
    participant R as Service Registry
    participant S1 as Service Instance 1
    participant S2 as Service Instance 2
    C->>R: Where is Order Service?
    R->>C: [instance1:8080, instance2:8080]
    C->>C: Pick instance (round-robin)
    C->>S1: Request
    S1->>C: Response

sequenceDiagram
    participant C as Client Service
    participant LB as Load Balancer
    participant R as Service Registry
    participant S1 as Service Instance 1
    C->>LB: Request to Order Service
    LB->>R: Get healthy instances
    R->>LB: [instance1, instance2]
    LB->>S1: Forward request
    S1->>LB: Response
    LB->>C: Response

apiVersion: v1
kind: Service
metadata:
  name: order-service
spec:
  selector:
    app: order
  ports:
    - port: 80
      targetPort: 8080
---
# Client calls: http://order-service/api/orders
# Kubernetes DNS resolves to pod IPs

sequenceDiagram
    participant C as Client
    participant GW as Gateway
    participant OS as Order Service
    participant US as User Service
    participant PS as Product Service
    C->>GW: GET /dashboard
    par Parallel calls
        GW->>OS: GET /orders
        GW->>US: GET /user
        GW->>PS: GET /recommendations
    end
    OS->>GW: Orders data
    US->>GW: User data
    PS->>GW: Recommendations
    GW->>GW: Aggregate
    GW->>C: Combined response

plugins:
  - name: jwt
    config:
      claims_to_verify:
        - exp
        - iss
  - name: rate-limiting
    config:
      minute: 100
      policy: local
  - name: correlation-id
    config:
      header_name: X-Request-ID
      generator: uuid

graph LR
    subgraph Your Service
        DS[Domain Logic]
        ACL[ACL Adapter]
    end
    EXT[External API]
    DS --> ACL
    ACL --> EXT

// External API returns inconsistent format
public class LegacyInventoryResponse {
    private String sku_code;
    private int qty_avail;
    private String loc_id;
}

// Your clean domain model
public record StockLevel(
    ProductId productId,
    int availableQuantity,
    WarehouseId warehouseId
) {}

// ACL translates
public class InventoryAcl {
    private final LegacyInventoryClient client;

    public StockLevel getStockLevel(ProductId productId) {
        LegacyInventoryResponse response = client.getStock(productId.value());
        return new StockLevel(
            productId,
            response.getQty_avail(),
            new WarehouseId(response.getLoc_id())
        );
    }
}