Architectural Styles

This file explores different architectural styles and their applications in modern software development.

Monolithic Architecture

Overview

A monolithic architecture deploys all application components as a single deployable unit.

Characteristics

• Single deployable artifact
• Shared database
• Centralized business logic
• Direct in-process communication

Example Structure

monolithic-app/
├── src/
│   ├── controllers/
│   │   ├── UserController.java
│   │   ├── OrderController.java
│   │   └── ProductController.java
│   ├── services/
│   │   ├── UserService.java
│   │   ├── OrderService.java
│   │   └── ProductService.java
│   ├── repositories/
│   │   ├── UserRepository.java
│   │   ├── OrderRepository.java
│   │   └── ProductRepository.java
│   └── models/
│       ├── User.java
│       ├── Order.java
│       └── Product.java
├── database/
│   └── schema.sql
└── config/
    └── application.properties

Advantages

• Simple deployment: Single artifact to deploy
• Easy testing: Everything runs in one process
• Simple debugging: All code in one place
• No network latency: Direct method calls
• ACID transactions: Easy to maintain consistency

Disadvantages

• Technology lock-in: Entire app uses same stack
• Scaling limitations: Must scale entire application
• Development bottlenecks: Large teams working on same codebase
• Fault tolerance: Single point of failure
• Deployment risk: Changes affect entire system

When to Use

• Small to medium applications
• Simple business domains
• Small development teams
• Rapid prototyping
• Applications with strong consistency requirements

Microservices Architecture

Overview

Microservices architecture structures an application as a collection of loosely coupled, independently deployable services.

Characteristics

• Service per business capability
• Decentralized governance
• Independent deployment
• Technology diversity
• Failure isolation

Example Structure

microservices-ecommerce/
├── user-service/
│   ├── src/main/java/
│   ├── Dockerfile
│   └── k8s/
├── order-service/
│   ├── src/main/java/
│   ├── Dockerfile
│   └── k8s/
├── product-service/
│   ├── src/main/java/
│   ├── Dockerfile
│   └── k8s/
├── notification-service/
│   ├── src/main/java/
│   ├── Dockerfile
│   └── k8s/
├── api-gateway/
│   ├── src/main/java/
│   ├── Dockerfile
│   └── k8s/
└── docker-compose.yml

Service Communication Patterns

Advantages

• Technology diversity: Each service can use different technologies
• Independent scaling: Scale services independently
• Fault isolation: Failure in one service doesn't bring down others
• Team autonomy: Teams can work independently
• Faster deployment: Deploy services independently

Disadvantages

• Distributed system complexity: Network calls, latency, failures
• Data consistency: Managing transactions across services
• Testing complexity: Integration testing is harder
• Operational overhead: More services to monitor and maintain
• Development overhead: Service discovery, configuration management

When to Use

• Large, complex applications
• Multiple development teams
• Different scaling requirements per component
• Need for technology diversity
• Organizations with DevOps maturity

Service-Oriented Architecture (SOA)

Overview

SOA is an architectural pattern where application components provide services through well-defined interfaces.

Characteristics

• Service contracts and interfaces
• Service registry and discovery
• Loose coupling
• Service composition
• Platform independence

SOA vs Microservices

Aspect	SOA	Microservices
Service Size	Larger services	Small, focused services
Communication	SOAP, ESB	HTTP/REST, messaging
Data Sharing	Shared databases	Database per service
Governance	Centralized	Decentralized

Serverless Architecture

Overview

Serverless architecture runs applications in stateless compute containers managed by cloud providers.

Characteristics

• No server management
• Event-driven execution
• Automatic scaling
• Pay-per-execution
• Stateless functions

Advantages

• No infrastructure management: Focus on business logic
• Automatic scaling: Scales with demand
• Cost effective: Pay only for execution time
• High availability: Built-in fault tolerance
• Fast deployment: Quick to deploy functions

Disadvantages

• Cold start latency: Initial execution delay
• Execution limits: Time and memory constraints
• Vendor lock-in: Platform-specific implementations
• Limited local testing: Hard to replicate cloud environment
• Debugging complexity: Distributed logging and monitoring

Event-Driven Architecture

Overview

Event-driven architecture uses events to trigger and communicate between decoupled services.

Components

• Event Producers: Generate events
• Event Routers: Route events to consumers
• Event Consumers: Process events
• Event Store: Persist events

Implementation Patterns

CQRS (Command Query Responsibility Segregation)

// Command side
public interface Command {
}

public class CreateUserCommand implements Command {
    private final String email;
    private final String firstName;
    private final String lastName;

    // Constructor and getters
}

@Service
public class UserCommandHandler {
    private final UserEventStore eventStore;

    public void handle(CreateUserCommand command) {
        String userId = UUID.randomUUID().toString();

        UserCreatedEvent event = new UserCreatedEvent(
            userId,
            command.getEmail(),
            command.getFirstName(),
            command.getLastName()
        );

        eventStore.saveEvent(userId, event);
    }
}

// Query side
@Entity
@Table(name = "user_view")
public class UserView {
    @Id
    private String id;
    private String email;
    private String fullName;
    private LocalDateTime createdAt;
    private LocalDateTime updatedAt;

    // Constructors, getters, setters
}

@Service
public class UserQueryHandler {
    private final UserViewRepository repository;

    @EventListener
    public void on(UserCreatedEvent event) {
        UserView view = new UserView();
        view.setId(event.getUserId());
        view.setEmail(event.getEmail());
        view.setFullName(event.getFirstName() + " " + event.getLastName());
        view.setCreatedAt(event.getOccurredOn());
        view.setUpdatedAt(event.getOccurredOn());

        repository.save(view);
    }

    @EventListener
    public void on(UserEmailChangedEvent event) {
        UserView view = repository.findById(event.getUserId())
            .orElseThrow(() -> new IllegalStateException("User view not found"));

        view.setEmail(event.getNewEmail());
        view.setUpdatedAt(event.getOccurredOn());

        repository.save(view);
    }

    public Optional<UserView> findById(String id) {
        return repository.findById(id);
    }

    public List<UserView> findByEmail(String email) {
        return repository.findByEmailContaining(email);
    }
}

Layered Architecture

Overview

Layered architecture organizes code into horizontal layers with each layer only communicating with the layer directly below it.

Common Layers

1. Presentation Layer: UI, Controllers
2. Business/Service Layer: Business logic
3. Persistence Layer: Data access
4. Database Layer: Data storage

Hexagonal Architecture (Ports and Adapters)

Overview

Hexagonal architecture isolates the core business logic from external concerns using ports and adapters.

Components

• Domain: Core business logic
• Ports: Interfaces for communication
• Adapters: Implementations of ports

Choosing the Right Architecture

Decision Matrix

Architecture	Team Size	Complexity	Scalability	Technology Diversity	Operational Complexity
Monolithic	Small	Low	Limited	Low	Low
Modular Monolith	Medium	Medium	Medium	Low	Low
Microservices	Large	High	High	High	High
Serverless	Variable	Medium	High	Medium	Medium

Guidelines

1. Start Simple: Begin with monolithic architecture
2. Evolve Gradually: Extract services when clear boundaries emerge
3. Consider Team Structure: Conway's Law applies
4. Evaluate Operational Capability: Can you manage distributed systems?
5. Business Requirements: Does your domain benefit from service boundaries?

Each architectural style has its place. Choose based on your specific context, team capabilities, and business requirements rather than following trends.