Advanced Patterns and Techniques

1. The Strangler Fig Pattern

Gradually replace specific functions of the monolith with microservices, allowing the two to coexist during migration.

Implementation Steps:

1. Identify Boundaries: Define clear service boundaries based on business capabilities
2. Create APIs: Build APIs around the identified boundaries within the monolith
3. Extract Services: Implement new services that replicate the functionality behind these APIs
4. Redirect Traffic: Gradually redirect traffic from the monolith to the new services
5. Remove Code: Once a service is fully migrated, remove the corresponding code from the monolith

Example Implementation:

// Step 1: Create an API facade in the monolith
@RestController
@RequestMapping("/api/products")
public class ProductController {
    @Autowired
    private ProductService productService;
    
    @GetMapping("/{id}")
    public Product getProduct(@PathVariable Long id) {
        return productService.getProduct(id);
    }
    
    // Other product endpoints...
}

// Step 2: Implement a routing facade that can direct to either the monolith or the new service
@Component
public class ProductRoutingFacade {
    @Autowired
    private ProductService legacyProductService;
    
    @Autowired
    private ProductServiceClient newProductServiceClient;
    
    @Value("${feature.flags.use-new-product-service}")
    private boolean useNewProductService;
    
    public Product getProduct(Long id) {
        if (useNewProductService) {
            return newProductServiceClient.getProduct(id);
        } else {
            return legacyProductService.getProduct(id);
        }
    }
    
    // Other product methods...
}

// Step 3: Update the controller to use the routing facade
@RestController
@RequestMapping("/api/products")
public class ProductController {
    @Autowired
    private ProductRoutingFacade productFacade;
    
    @GetMapping("/{id}")
    public Product getProduct(@PathVariable Long id) {
        return productFacade.getProduct(id);
    }
    
    // Other product endpoints...
}

2. Domain-Driven Decomposition

Use Domain-Driven Design (DDD) principles to identify bounded contexts that can become microservices.

Implementation Steps:

1. Analyze Domain: Identify bounded contexts and aggregates within your domain
2. Define Context Maps: Understand relationships between different bounded contexts
3. Refactor Monolith: Reorganize the monolith’s internal structure to align with these contexts
4. Extract Services: Extract one bounded context at a time into separate services
5. Establish Communication: Implement appropriate communication patterns between services

Example Domain Analysis:

E-commerce Domain Bounded Contexts:
1. Product Catalog
   - Aggregates: Product, Category, Brand
   - Commands: CreateProduct, UpdateProduct, DiscontinueProduct
   - Queries: GetProduct, SearchProducts, GetProductsByCategory

2. Order Management
   - Aggregates: Order, OrderItem, ShippingInfo
   - Commands: CreateOrder, UpdateOrderStatus, CancelOrder
   - Queries: GetOrder, GetOrderHistory, GetOrdersByCustomer

3. Customer Management
   - Aggregates: Customer, Address, PaymentMethod
   - Commands: RegisterCustomer, UpdateCustomerInfo, AddPaymentMethod
   - Queries: GetCustomer, GetCustomerOrders, ValidateCustomer

4. Inventory Management
   - Aggregates: Inventory, Warehouse, StockMovement
   - Commands: ReceiveStock, AllocateStock, AdjustInventory
   - Queries: GetProductAvailability, GetWarehouseStock

3. The Sidecar Pattern

Deploy new functionality as services that run alongside the monolith, gradually moving functionality out of the monolith.

Implementation Steps:

1. Identify New Features: Select new features that can be implemented as separate services
2. Implement Services: Build these features as independent services
3. Integrate with Monolith: Use APIs or event-based communication to integrate with the monolith
4. Gradually Refactor: Over time, move existing functionality from the monolith to new services

Example Architecture:

# Docker Compose example of sidecar pattern
version: '3'
services:
  monolith:
    image: e-commerce-monolith:latest
    ports:
      - "8080:8080"
    environment:
      - RECOMMENDATION_SERVICE_URL=http://recommendation-service:8081
      - SEARCH_SERVICE_URL=http://search-service:8082
    depends_on:
      - recommendation-service
      - search-service
  
  recommendation-service:
    image: recommendation-service:latest
    ports:
      - "8081:8081"
    environment:
      - SPRING_PROFILES_ACTIVE=production
  
  search-service:
    image: search-service:latest
    ports:
      - "8082:8082"
    environment:
      - ELASTICSEARCH_URL=http://elasticsearch:9200
    depends_on:
      - elasticsearch
  
  elasticsearch:
    image: elasticsearch:7.10.0
    ports:
      - "9200:9200"
    environment:
      - discovery.type=single-node

Real-World Case Studies

Let’s examine how different organizations have approached the monolith vs. microservices decision.

Case Study 1: Amazon’s Journey to Microservices

Initial State: Amazon started with a monolithic application that handled all aspects of their e-commerce platform.

Challenges:

• Scaling the development organization
• Slow deployment cycles
• Difficulty scaling specific components independently

Migration Approach:

• Gradual decomposition into services
• Service-oriented architecture with clear APIs
• “Two-pizza teams” (teams small enough to be fed by two pizzas)

Results:

• Thousands of microservices
• Multiple deployments per second
• Teams can innovate independently
• Highly resilient and scalable platform

Key Lesson: Microservices enabled Amazon to scale both technically and organizationally, but the transition was gradual and pragmatic.

Case Study 2: Shopify’s Modular Monolith

Initial State: Shopify built their e-commerce platform as a Ruby on Rails monolith.

Approach:

• Maintained a monolithic architecture
• Focused on internal modularity
• Invested heavily in tooling and infrastructure
• Extracted specific components as services only when necessary

Results:

• Successfully scaled to support millions of merchants
• Maintained developer productivity
• Avoided unnecessary operational complexity
• Extracted only specific components (e.g., Storefront Renderer) as services

Key Lesson: A well-designed monolith with clear internal boundaries can scale effectively for many organizations.