distributed-events-advanced

Distributed Events Advanced Patterns

Master advanced distributed event patterns for building resilient, scalable ABP microservices architectures.

When to Use This Skill

• Implementing event handlers that process events from other microservices
• Building idempotent event processing to handle duplicates
• Cross-tenant event synchronization
• Designing event-driven communication patterns
• Implementing saga/choreography patterns
• Troubleshooting event delivery issues

Core Concepts

Event Transfer Objects (ETOs)

ETOs are the payload of distributed events. Define them in a shared library accessible by both publisher and subscriber.

// Shared/Etos/PatientCreatedEto.cs
[EventName("patient.created")]  // Optional: explicit event name
public class PatientCreatedEto
{
    public Guid Id { get; set; }
    public Guid? TenantId { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
    public DateTime CreatedAt { get; set; }

    // Include correlation ID for tracing
    public string CorrelationId { get; set; }
}

ETO Best Practices:

• Include TenantId for multi-tenant scenarios
• Include CorrelationId for distributed tracing
• Use primitive types only (no navigation properties)
• Version ETOs carefully (add properties, don't remove)

Event Handler Patterns

1. Basic Event Handler

public class PatientCreatedEventHandler :
    IDistributedEventHandler<PatientCreatedEto>,
    ITransientDependency
{
    private readonly ILogger<PatientCreatedEventHandler> _logger;

    public PatientCreatedEventHandler(
        ILogger<PatientCreatedEventHandler> logger)
    {
        _logger = logger;
    }

    public async Task HandleEventAsync(PatientCreatedEto eventData)
    {
        _logger.LogInformation(
            "Processing PatientCreated event: {PatientId}",
            eventData.Id);

        // Handle the event
        await ProcessPatientAsync(eventData);
    }
}

2. Idempotent Event Handler