event-driven

Event-Driven Architecture (EDA)

Event-Driven Architecture (EDA) is a distributed systems paradigm decoupling producers and consumers through asynchronous event streams, enabling horizontal scalability and fault-tolerant processing.

When to Use

• Decoupled Microservice Architectures: Connecting distributed services through asynchronous events rather than fragile synchronous HTTP chains.
• High-Volume Asynchronous Processing: Ingesting IoT telemetry, analytics events, and user activity logs with buffer-backed queues.
• Complex Cross-Service Workflows: Coordinating order processing, inventory reservations, and notifications asynchronously.
• Zero-Downtime Resilience: Ensuring systems continue functioning and queuing events even when consumer services are temporarily offline.

Quick Start

// Producer (Order Service)
await messageBroker.publish("order.created", {
  orderId: "123",
  userId: "456",
  timestamp: Date.now(),
});

// Consumer (Shipping Service)
// Doesn't need to be online when order is created
messageBroker.subscribe("order.created", async (event) => {
  await shippingService.schedulePickup(event.orderId);
  console.log("Shipping scheduled");
});

// Consumer (Analytics Service)
// New feature added later? No changes to Order Service!
messageBroker.subscribe("order.created", async (event) => {
  await analytics.trackRevenue(event);
});

Core Concepts

Pub/Sub Topology & Fan-Out

Producers publish events without knowing consumers; brokers fan out events to multiple subscriber queues:

[ Order Service ] ──Publish(OrderPlaced)──→ [ Topic: orders.events ]
                                                     ├──→ [ Queue: Inventory ] ──→ [ Inventory Service ]
                                                     ├──→ [ Queue: Billing ]   ──→ [ Payment Service ]
                                                     └──→ [ Queue: Email ]     ──→ [ Notification Service ]

CloudEvents Specification Standard