Event-Driven Architecture - Design Patterns and Implementation Strategies for Scalable Systems

Introduction

Event-driven architecture (EDA) has become the foundation for building scalable, loosely coupled distributed systems that can handle millions of events per second. By decoupling components through asynchronous event communication, EDA enables systems to scale independently, recover gracefully from failures, and adapt to changing business requirements without extensive refactoring.

This comprehensive guide explores event-driven architecture patterns, event sourcing and CQRS implementations, message broker strategies with Kafka and RabbitMQ, and production best practices from companies like Netflix, Uber, and LinkedIn that process billions of events daily.

Core Concepts of Event-Driven Architecture

Events vs Messages vs Commands

Understanding the distinction is crucial for proper EDA implementation:

// Event: Something that happened (past tense)
interface OrderPlacedEvent {
  eventId: string;
  eventType: 'OrderPlaced';
  timestamp: Date;
  aggregateId: string; // Order ID
  data: {
    orderId: string;
    customerId: string;
    items: OrderItem[];
    totalAmount: number;
  };
}
// Command: Intent to do something (imperative)
interface PlaceOrderCommand {
commandId: string;
commandType: 'PlaceOrder';
customerId: string;
items: OrderItem[];
paymentMethod: string;
}
// Message: Generic communication (can be event or command)
interface Message {
messageId: string;
messageType: string;
timestamp: Date;
payload: any;
metadata: {
correlationId: string;
causationId: string;
userId?: string;
};
}
// Event emitter pattern
class OrderService {
private eventBus: EventBus;
async placeOrder(command: PlaceOrderCommand): Promise<string> {
// Validate command
this.validateOrder(command);
// Create order
const order = await this.createOrder(command);

// Emit event (fire and forget)
await this.eventBus.publish({
  eventId: uuidv4(),
  eventType: 'OrderPlaced',
  timestamp: new Date(),
  aggregateId: order.id,
  data: {
    orderId: order.id,
    customerId: command.customerId,
    items: command.items,
    totalAmount: order.total
  }
});

return order.id;

}
}

Event Bus Implementation

A simple in-memory event bus for understanding the pattern:

type EventHandler<T> = (event: T) => Promise<void>;
class EventBus {
private handlers: Map<string, EventHandler<any>[]> = new Map();
private middleware: EventMiddleware[] = [];
subscribe<T>(eventType: string, handler: EventHandler<T>): void {
if (!this.handlers.has(eventType)) {
this.handlers.set(eventType, []);
}
this.handlers.get(eventType)!.push(handler);
}
async publish<T>(event: T & { eventType: string }): Promise<void> {
// Apply middleware
let processedEvent = event;
for (const mw of this.middleware) {
processedEvent = await mw.process(processedEvent);
}
// Get handlers for this event type
const handlers = this.handlers.get(event.eventType) || [];

// Execute handlers in parallel
await Promise.allSettled(
  handlers.map(async (handler) =&gt; {
    try {
      await handler(processedEvent);
    } catch (error) {
      console.error(`Handler error for ${event.eventType}:`, error);
      // Publish error event
      await this.publishError(event, error);
    }
  })
);

}
private async publishError(event: any, error: Error): Promise<void> {
await this.publish({
eventType: 'EventHandlerFailed',
originalEvent: event,
error: {
message: error.message,
stack: error.stack
},
timestamp: new Date()
});
}
use(middleware: EventMiddleware): void {
this.middleware.push(middleware);
}
}
// Usage with multiple subscribers
const eventBus = new EventBus();
// Inventory service listens for orders
eventBus.subscribe<OrderPlacedEvent>('OrderPlaced', async (event) => {
console.log('Inventory: Reserving items for order', event.data.orderId);
await inventoryService.reserveItems(event.data.items);
});
// Notification service listens for orders
eventBus.subscribe<OrderPlacedEvent>('OrderPlaced', async (event) => {
console.log('Notification: Sending confirmation email');
await notificationService.sendOrderConfirmation(event.data.customerId);
});
// Analytics service listens for orders
eventBus.subscribe<OrderPlacedEvent>('OrderPlaced', async (event) => {
console.log('Analytics: Recording order metrics');
await analyticsService.recordOrder(event.data);
});

Event Sourcing Pattern

Event sourcing stores all changes as a sequence of events, making the event log the source of truth:

// Event store interface
interface EventStore {
  append(streamId: string, events: Event[]): Promise<void>;
  getEvents(streamId: string, fromVersion?: number): Promise<Event[]>;
}
// Base event
interface Event {
eventId: string;
eventType: string;
timestamp: Date;
version: number;
data: any;
}
// Order aggregate using event sourcing
class OrderAggregate {
private id: string;
private version: number = 0;
private uncommittedEvents: Event[] = [];
// Current state
private customerId: string = '';
private items: OrderItem[] = [];
private status: OrderStatus = 'pending';
private totalAmount: number = 0;
constructor(id: string)
// Command: Place order
placeOrder(customerId: string, items: OrderItem[]): void {
if (this.status !== 'pending') {
throw new Error('Order already placed');
}
const totalAmount = items.reduce((sum, item) =&gt;
  sum + (item.price * item.quantity), 0
);

this.applyEvent({
  eventId: uuidv4(),
  eventType: 'OrderPlaced',
  timestamp: new Date(),
  version: this.version + 1,
  data: {
    orderId: this.id,
    customerId,
    items,
    totalAmount
  }
});

}
// Command: Confirm payment
confirmPayment(paymentId: string, amount: number): void {
if (this.status !== 'pending') {
throw new Error('Invalid order status for payment');
}
if (amount !== this.totalAmount) {
  throw new Error('Payment amount mismatch');
}

this.applyEvent({
  eventId: uuidv4(),
  eventType: 'PaymentConfirmed',
  timestamp: new Date(),
  version: this.version + 1,
  data: {
    orderId: this.id,
    paymentId,
    amount
  }
});

}
// Command: Ship order
shipOrder(trackingNumber: string): void {
if (this.status !== 'paid') {
throw new Error('Cannot ship unpaid order');
}
this.applyEvent({
  eventId: uuidv4(),
  eventType: 'OrderShipped',
  timestamp: new Date(),
  version: this.version + 1,
  data: {
    orderId: this.id,
    trackingNumber,
    shippedAt: new Date()
  }
});

}
// Apply event to change state
private applyEvent(event: Event): void {
// Update state based on event
this.apply(event);
// Track uncommitted event
this.uncommittedEvents.push(event);

// Increment version
this.version = event.version;

}
// State mutations based on events
private apply(event: Event): void {
switch (event.eventType) {
case 'OrderPlaced':
this.customerId = event.data.customerId;
this.items = event.data.items;
this.totalAmount = event.data.totalAmount;
this.status = 'pending';
break;
  case 'PaymentConfirmed':
    this.status = 'paid';
    break;

  case 'OrderShipped':
    this.status = 'shipped';
    break;

  case 'OrderCancelled':
    this.status = 'cancelled';
    break;
}

}
// Rebuild state from events (event replay)
static async load(
eventStore: EventStore,
orderId: string
): Promise<OrderAggregate> {
const aggregate = new OrderAggregate(orderId);
const events = await eventStore.getEvents(orderId);
for (const event of events) {
  aggregate.apply(event);
  aggregate.version = event.version;
}

return aggregate;

}
// Get uncommitted events
getUncommittedEvents(): Event[] {
return this.uncommittedEvents;
}
// Mark events as committed
markEventsAsCommitted(): void
// Getters
getId(): string { return this.id; }
getStatus(): OrderStatus { return this.status; }
getTotalAmount(): number { return this.totalAmount; }
}
// Repository pattern with event store
class OrderRepository {
constructor(private eventStore: EventStore) {}
async save(order: OrderAggregate): Promise<void> {
const events = order.getUncommittedEvents();
if (events.length === 0) {
  return;
}

await this.eventStore.append(order.getId(), events);
order.markEventsAsCommitted();

}
async getById(orderId: string): Promise<OrderAggregate> {
return OrderAggregate.load(this.eventStore, orderId);
}
}

Event Store Implementation with PostgreSQL

class PostgresEventStore implements EventStore {
  constructor(private pool: Pool) {}
async append(streamId: string, events: Event[]): Promise<void> {
const client = await this.pool.connect();
try {
  await client.query('BEGIN');

  for (const event of events) {
    await client.query(
      `INSERT INTO events (
        event_id, stream_id, event_type, version,
        data, metadata, created_at
      ) VALUES ($1, $2, $3, $4, $5, $6, $7)`,
      [
        event.eventId,
        streamId,
        event.eventType,
        event.version,
        JSON.stringify(event.data),
        JSON.stringify({ timestamp: event.timestamp }),
        event.timestamp
      ]
    );
  }

  await client.query('COMMIT');
} catch (error) {
  await client.query('ROLLBACK');
  throw error;
} finally {
  client.release();
}

}
async getEvents(
streamId: string,
fromVersion: number = 0
): Promise<Event[]> {
const result = await this.pool.query(
SELECT event_id, event_type, version, data, created_at FROM events WHERE stream_id = $1 AND version &gt; $2 ORDER BY version ASC,
[streamId, fromVersion]
);
return result.rows.map(row =&gt; ({
  eventId: row.event_id,
  eventType: row.event_type,
  version: row.version,
  timestamp: row.created_at,
  data: row.data
}));

}
async getAllEvents(fromPosition: number = 0): Promise<Event[]> {
const result = await this.pool.query(
SELECT event_id, stream_id, event_type, version, data, created_at FROM events WHERE id &gt; $1 ORDER BY id ASC LIMIT 1000,
[fromPosition]
);
return result.rows.map(row =&gt; ({
  eventId: row.event_id,
  eventType: row.event_type,
  version: row.version,
  timestamp: row.created_at,
  data: row.data
}));

}
}
// Database schema
const eventStoreSchema = `
CREATE TABLE events (
id BIGSERIAL PRIMARY KEY,
event_id UUID NOT NULL UNIQUE,
stream_id VARCHAR(255) NOT NULL,
event_type VARCHAR(255) NOT NULL,
version INTEGER NOT NULL,
data JSONB NOT NULL,
metadata JSONB,
created_at TIMESTAMP NOT NULL DEFAULT NOW(),
UNIQUE (stream_id, version)
);
CREATE INDEX idx_events_stream_id ON events(stream_id);
CREATE INDEX idx_events_event_type ON events(event_type);
CREATE INDEX idx_events_created_at ON events(created_at);
`;

CQRS (Command Query Responsibility Segregation)

Separate read and write models for optimized performance:

// Write model (command side)
class OrderCommandHandler {
  constructor(
    private repository: OrderRepository,
    private eventBus: EventBus
  ) {}
async handle(command: PlaceOrderCommand): Promise<string> {
// Create new aggregate
const order = new OrderAggregate(uuidv4());
// Execute command
order.placeOrder(command.customerId, command.items);

// Save to event store
await this.repository.save(order);

// Publish events to event bus
const events = order.getUncommittedEvents();
for (const event of events) {
  await this.eventBus.publish(event);
}

return order.getId();

}
}
// Read model (query side)
interface OrderReadModel {
orderId: string;
customerId: string;
customerName: string;
totalAmount: number;
status: string;
items: OrderItem[];
createdAt: Date;
updatedAt: Date;
}
class OrderReadModelRepository {
constructor(private pool: Pool) {}
async getById(orderId: string): Promise<OrderReadModel | null> {
const result = await this.pool.query(
SELECT * FROM order_read_model WHERE order_id = $1,
[orderId]
);
return result.rows[0] || null;

}
async getByCustomer(customerId: string): Promise<OrderReadModel[]> {
const result = await this.pool.query(
SELECT * FROM order_read_model WHERE customer_id = $1 ORDER BY created_at DESC,
[customerId]
);
return result.rows;

}
async update(order: OrderReadModel): Promise<void> {
await this.pool.query(
INSERT INTO order_read_model ( order_id, customer_id, customer_name, total_amount, status, items, created_at, updated_at ) VALUES ($1, $2, $3, $4, $5, $6, $7, $8) ON CONFLICT (order_id) DO UPDATE SET status = $5, updated_at = $8,
[
order.orderId,
order.customerId,
order.customerName,
order.totalAmount,
order.status,
JSON.stringify(order.items),
order.createdAt,
order.updatedAt
]
);
}
}
// Projections: Update read model from events
class OrderProjection {
constructor(
private readRepository: OrderReadModelRepository,
private customerService: CustomerService
) {}
async onOrderPlaced(event: OrderPlacedEvent): Promise<void> {
const customer = await this.customerService.getById(
event.data.customerId
);
await this.readRepository.update({
  orderId: event.data.orderId,
  customerId: event.data.customerId,
  customerName: customer.name,
  totalAmount: event.data.totalAmount,
  status: 'pending',
  items: event.data.items,
  createdAt: event.timestamp,
  updatedAt: event.timestamp
});

}
async onPaymentConfirmed(event: PaymentConfirmedEvent): Promise<void> {
const order = await this.readRepository.getById(event.data.orderId);
if (order) {
  order.status = 'paid';
  order.updatedAt = event.timestamp;
  await this.readRepository.update(order);
}

}
async onOrderShipped(event: OrderShippedEvent): Promise<void> {
const order = await this.readRepository.getById(event.data.orderId);
if (order) {
  order.status = 'shipped';
  order.updatedAt = event.timestamp;
  await this.readRepository.update(order);
}

}
}
// Wire up projections to event bus
const projection = new OrderProjection(readRepository, customerService);
eventBus.subscribe<OrderPlacedEvent>(
'OrderPlaced',
(e) => projection.onOrderPlaced(e)
);
eventBus.subscribe<PaymentConfirmedEvent>(
'PaymentConfirmed',
(e) => projection.onPaymentConfirmed(e)
);
eventBus.subscribe<OrderShippedEvent>(
'OrderShipped',
(e) => projection.onOrderShipped(e)
);

Message Brokers

Apache Kafka Implementation

Kafka provides durable, scalable event streaming:

import { Kafka, Producer, Consumer, EachMessagePayload } from 'kafkajs';
class KafkaEventBus {
private kafka: Kafka;
private producer: Producer;
private consumers: Map<string, Consumer> = new Map();
constructor(brokers: string[]) {
this.kafka = new Kafka({
clientId: 'order-service',
brokers,
retry: {
initialRetryTime: 100,
retries: 8
}
});
this.producer = this.kafka.producer({
  idempotent: true,
  maxInFlightRequests: 5,
  transactionalId: 'order-service-producer'
});

}
async connect(): Promise<void> {
await this.producer.connect();
}
async publish(topic: string, event: Event): Promise<void> {
await this.producer.send({
topic,
messages: [
{
key: event.data.orderId || event.eventId,
value: JSON.stringify(event),
headers: {
eventType: event.eventType,
eventId: event.eventId,
timestamp: event.timestamp.toISOString()
}
}
]
});
}
async publishBatch(topic: string, events: Event[]): Promise<void> {
const transaction = await this.producer.transaction();
try {
  await transaction.send({
    topic,
    messages: events.map(event =&gt; ({
      key: event.data.orderId || event.eventId,
      value: JSON.stringify(event),
      headers: {
        eventType: event.eventType,
        eventId: event.eventId,
        timestamp: event.timestamp.toISOString()
      }
    }))
  });

  await transaction.commit();
} catch (error) {
  await transaction.abort();
  throw error;
}

}
async subscribe(
groupId: string,
topic: string,
handler: (event: Event) => Promise<void>
): Promise<void> {
const consumer = this.kafka.consumer({
groupId,
sessionTimeout: 30000,
heartbeatInterval: 3000
});
await consumer.connect();
await consumer.subscribe({ topic, fromBeginning: false });

await consumer.run({
  eachMessage: async ({ message, partition }: EachMessagePayload) =&gt; {
    const event = JSON.parse(message.value!.toString());

    try {
      await handler(event);
    } catch (error) {
      console.error(`Error processing event ${event.eventId}:`, error);

      // Send to dead letter queue
      await this.sendToDeadLetterQueue(topic, event, error);
    }
  }
});

this.consumers.set(groupId, consumer);

}
private async sendToDeadLetterQueue(
originalTopic: string,
event: Event,
error: Error
): Promise<void> {
await this.producer.send({
topic: ${originalTopic}.dead-letter,
messages: [
{
key: event.eventId,
value: JSON.stringify({
originalEvent: event,
error: {
message: error.message,
stack: error.stack
},
failedAt: new Date()
})
}
]
});
}
async disconnect(): Promise<void> {
await this.producer.disconnect();
for (const consumer of this.consumers.values()) {
  await consumer.disconnect();
}

}
}
// Usage
const kafka = new KafkaEventBus(['localhost:9092']);
await kafka.connect();
// Publish events
await kafka.publish('orders', {
eventId: uuidv4(),
eventType: 'OrderPlaced',
timestamp: new Date(),
data: { orderId: '123', customerId: 'customer-1' }
});
// Subscribe to events
await kafka.subscribe(
'inventory-service',
'orders',
async (event) => {
console.log('Processing order event:', event);
await inventoryService.processOrder(event.data);
}
);

RabbitMQ Implementation

RabbitMQ provides flexible routing with exchanges and queues:

import amqp, { Connection, Channel, ConsumeMessage } from 'amqplib';
class RabbitMQEventBus {
private connection: Connection | null = null;
private publishChannel: Channel | null = null;
private consumeChannels: Map<string, Channel> = new Map();
async connect(url: string): Promise<void> {
this.connection = await amqp.connect(url);
this.publishChannel = await this.connection.createChannel();
// Declare exchange
await this.publishChannel.assertExchange('events', 'topic', {
  durable: true
});

}
async publish(routingKey: string, event: Event): Promise<void> {
if (!this.publishChannel) {
throw new Error('Not connected');
}
this.publishChannel.publish(
  'events',
  routingKey,
  Buffer.from(JSON.stringify(event)),
  {
    persistent: true,
    contentType: 'application/json',
    messageId: event.eventId,
    timestamp: event.timestamp.getTime(),
    headers: {
      eventType: event.eventType
    }
  }
);

}
async subscribe(
queueName: string,
routingPattern: string,
handler: (event: Event) => Promise<void>,
options: { prefetch?: number; retry?: boolean } = {}
): Promise<void> {
if (!this.connection) {
throw new Error('Not connected');
}
const channel = await this.connection.createChannel();
this.consumeChannels.set(queueName, channel);

// Set prefetch count for fair dispatch
await channel.prefetch(options.prefetch || 10);

// Declare queue
await channel.assertQueue(queueName, {
  durable: true,
  arguments: {
    'x-max-priority': 10,
    ...(options.retry &amp;&amp; {
      'x-dead-letter-exchange': 'events.retry',
      'x-dead-letter-routing-key': `retry.${routingPattern}`
    })
  }
});

// Bind queue to exchange
await channel.bindQueue(queueName, 'events', routingPattern);

// Consume messages
await channel.consume(
  queueName,
  async (message: ConsumeMessage | null) =&gt; {
    if (!message) return;

    const event = JSON.parse(message.content.toString());

    try {
      await handler(event);
      channel.ack(message);
    } catch (error) {
      console.error(`Error processing event ${event.eventId}:`, error);

      // Retry logic
      const retryCount = message.properties.headers['x-retry-count'] || 0;

      if (retryCount &lt; 3) {
        // Requeue with exponential backoff
        const delay = Math.pow(2, retryCount) * 1000;

        setTimeout(() =&gt; {
          channel.nack(message, false, true);
        }, delay);
      } else {
        // Move to dead letter queue
        channel.nack(message, false, false);
      }
    }
  },
  { noAck: false }
);

}
async disconnect(): Promise<void> {
for (const channel of this.consumeChannels.values()) {
await channel.close();
}
if (this.publishChannel) {
  await this.publishChannel.close();
}

if (this.connection) {
  await this.connection.close();
}

}
}
// Usage with routing patterns
const rabbitmq = new RabbitMQEventBus();
await rabbitmq.connect('amqp://localhost');
// Publish with routing key
await rabbitmq.publish('order.placed', orderPlacedEvent);
await rabbitmq.publish('order.shipped', orderShippedEvent);
await rabbitmq.publish('payment.confirmed', paymentConfirmedEvent);
// Subscribe with pattern matching
await rabbitmq.subscribe(
'inventory-service',
'order.*',  // All order events
async (event) => {
await inventoryService.handleOrderEvent(event);
}
);
await rabbitmq.subscribe(
'notification-service',
'*.placed',  // All placed events
async (event) => {
await notificationService.sendNotification(event);
}
);

Saga Pattern for Distributed Transactions

Coordinate long-running transactions across multiple services:

interface SagaStep {
  execute: () => Promise<void>;
  compensate: () => Promise<void>;
}
class Saga {
private steps: SagaStep[] = [];
private executedSteps: SagaStep[] = [];
addStep(step: SagaStep): void {
this.steps.push(step);
}
async execute(): Promise<void> {
try {
for (const step of this.steps) {
await step.execute();
this.executedSteps.push(step);
}
} catch (error) {
console.error('Saga execution failed, compensating:', error);
await this.compensate();
throw error;
}
}
private async compensate(): Promise<void> {
// Execute compensations in reverse order
for (const step of this.executedSteps.reverse()) {
try {
await step.compensate();
} catch (error) {
console.error('Compensation failed:', error);
// Continue with other compensations
}
}
}
}
// Order saga example
class OrderSaga {
constructor(
private orderService: OrderService,
private paymentService: PaymentService,
private inventoryService: InventoryService,
private shippingService: ShippingService
) {}
async placeOrder(orderData: PlaceOrderCommand): Promise<string> {
let orderId: string;
let paymentId: string;
let reservationId: string;
let shippingId: string;
const saga = new Saga();

// Step 1: Create order
saga.addStep({
  execute: async () =&gt; {
    orderId = await this.orderService.createOrder(orderData);
  },
  compensate: async () =&gt; {
    await this.orderService.cancelOrder(orderId);
  }
});

// Step 2: Process payment
saga.addStep({
  execute: async () =&gt; {
    paymentId = await this.paymentService.processPayment({
      orderId,
      amount: orderData.totalAmount,
      paymentMethod: orderData.paymentMethod
    });
  },
  compensate: async () =&gt; {
    await this.paymentService.refundPayment(paymentId);
  }
});

// Step 3: Reserve inventory
saga.addStep({
  execute: async () =&gt; {
    reservationId = await this.inventoryService.reserveItems({
      orderId,
      items: orderData.items
    });
  },
  compensate: async () =&gt; {
    await this.inventoryService.releaseReservation(reservationId);
  }
});

// Step 4: Create shipment
saga.addStep({
  execute: async () =&gt; {
    shippingId = await this.shippingService.createShipment({
      orderId,
      address: orderData.shippingAddress
    });
  },
  compensate: async () =&gt; {
    await this.shippingService.cancelShipment(shippingId);
  }
});

// Execute saga
await saga.execute();

return orderId;

}
}

Production Best Practices

Event Versioning

Handle event schema evolution:

interface EventV1 {
  version: 1;
  eventType: 'OrderPlaced';
  data: {
    orderId: string;
    customerId: string;
    amount: number;
  };
}
interface EventV2 {
version: 2;
eventType: 'OrderPlaced';
data: {
orderId: string;
customerId: string;
items: OrderItem[];
totalAmount: number;
currency: string;
};
}
class EventUpgrader {
upgrade(event: EventV1 | EventV2): EventV2 {
if (event.version === 2) {
return event;
}
// Upgrade v1 to v2
return {
  version: 2,
  eventType: event.eventType,
  data: {
    orderId: event.data.orderId,
    customerId: event.data.customerId,
    items: [], // Unknown in v1
    totalAmount: event.data.amount,
    currency: 'USD' // Default
  }
};

}
}

Idempotency

Ensure event handlers can be safely retried:

class IdempotentEventHandler {
  constructor(private redis: Redis) {}
async handle(event: Event, handler: () => Promise<void>): Promise<void> {
const key = processed:${event.eventId};
// Check if already processed
const processed = await this.redis.get(key);
if (processed) {
  console.log(`Event ${event.eventId} already processed`);
  return;
}

// Process event
await handler();

// Mark as processed (expire after 7 days)
await this.redis.setex(key, 604800, '1');

}
}

Real-World Examples

Netflix Event-Driven Architecture

Netflix processes 500+ billion events per day:

// Simulated Netflix-style event processing
class NetflixEventProcessor {
  async processViewEvent(event: VideoViewEvent): Promise<void> {
    // Parallel processing
    await Promise.all([
      this.updateWatchHistory(event),
      this.updateRecommendations(event),
      this.trackEngagement(event),
      this.updateTrending(event)
    ]);
  }
private async updateWatchHistory(event: VideoViewEvent): Promise<void> {
// Update user's watch history
}
private async updateRecommendations(event: VideoViewEvent): Promise<void> {
// Trigger recommendation recalculation
}
private async trackEngagement(event: VideoViewEvent): Promise<void> {
// Track engagement metrics
}
private async updateTrending(event: VideoViewEvent): Promise<void> {
// Update trending algorithms
}
}

Conclusion

Event-driven architecture enables building scalable, resilient distributed systems by decoupling components through asynchronous event communication. Implement event sourcing for complete audit trails, use CQRS for optimized read/write models, leverage message brokers like Kafka for reliable event delivery, and apply saga patterns for distributed transactions.

Key takeaways:

• Events represent facts that happened, commands represent intent
• Event sourcing makes events the source of truth
• CQRS separates read and write models for performance
• Kafka provides durable, ordered event streams at scale
• RabbitMQ offers flexible routing with exchanges and queues
• Saga pattern coordinates distributed transactions
• Handle event versioning, idempotency, and failure scenarios

Production systems like Netflix process 500+ billion events daily with 99.99% reliability using event-driven architectures with Kafka, while Uber's event-driven platform handles 100+ trillion events per year across 4,000+ microservices.