Lesson 2: Domain Events & Event Modeling

In-depth Event-Driven Microservices architecture

Part 1: Event-Driven Foundations

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Introduction

Domain Events in DDD. Event Storming workshop. Event Modeling technique. Identifying events, commands, aggregates. Event naming conventions.

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1. Domain Events in DDD

1.1 Basic concepts

Domain Events in DDD is one of the most important topics in this field. Understanding the core concepts will help you design the right system from the beginning.

Key Concepts:
├── Concept 1: Nền tảng lý thuyết
├── Concept 2: Áp dụng thực tế
├── Concept 3: Best practices
└── Concept 4: Anti-patterns cần tránh

1.2 Why is it important?

Aspect	Not applicable	Correct application
Performance	Bottlenecks, high latency	Optimized, scalable
Reliability	Single point of failure	Fault-tolerant
Maintainability	Technical debt accumulated	Clean architecture
Security	Vulnerable	Defense in depth

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2. Event Storming workshop

2.1 General architecture

┌─────────────────────────────────────────────────────┐
│                  SYSTEM ARCHITECTURE                 │
│                                                      │
│  ┌──────────┐  ┌──────────┐  ┌──────────────────┐  │
│  │  Client   │  │  API     │  │  Core Service    │  │
│  │  Layer    │──│  Gateway │──│  Layer           │  │
│  └──────────┘  └──────────┘  └──────────────────┘  │
│                                      │               │
│                               ┌──────▼──────┐       │
│                               │  Data Layer │       │
│                               └─────────────┘       │
└─────────────────────────────────────────────────────┘

2.2 Component Design

Each component in the system needs to be designed with the following principles:

• Single Responsibility: Each component only takes on one responsibility
• Loose Coupling: Minimize dependencies between components
• High Cohesion: Related elements are in the same component
• Interface Segregation: Clear, separate API

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3. Event Modeling technique

3.1 Design Patterns applied

Applied Patterns:
├── Strategy Pattern: Cho phép thay đổi algorithm at runtime
├── Observer Pattern: Event notification mechanism
├── Repository Pattern: Data access abstraction
└── Factory Pattern: Object creation flexibility

3.2 Code Example

// Example implementation
public interface Service {
    Result process(Request request);
    boolean supports(RequestType type);
}

@Component
public class CoreService implements Service {

    @Override
    public Result process(Request request) {
        // Validate input
        validator.validate(request);

        // Execute business logic
        var result = businessLogic.execute(request);

        // Publish domain event
        eventBus.publish(new ProcessedEvent(result));

        return result;
    }
}

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4. Identifying events, commands, aggregates

4.1 Monitoring & Observability

Observability Stack:
├── Metrics: Prometheus + Grafana
├── Logging: ELK / Loki
├── Tracing: OpenTelemetry + Jaeger
└── Alerting: PagerDuty

4.2 Performance Optimization

Metrics	Target	Strategy
Latency p99	< 100ms	Caching, async processing
Throughput	> 10K RPS	Horizontal scaling
Availability	99.99%	Multi-region, failover
Error rate	< 0.01%	Circuit breaker, retry

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Summary

In this lesson, we learned about Domain Events & Event Modeling. Key takeaways:

• Understand core concepts and how to apply
• Design architecture in accordance with requirements
• Implementation patterns and best practices
• Production considerations: monitoring, performance, security

Next article: We will continue with the next topic in the series.