I’ve spent the last few years building systems that need to handle thousands of events per second while maintaining data consistency. The challenge of creating resilient, scalable architectures led me to combine TypeScript’s type safety with Redis Streams’ persistence. This approach transformed how I design distributed systems, and I want to share the practical implementation that saved countless debugging hours.

Have you ever faced a situation where a minor event processing error cascaded into system-wide failures? That painful experience drove me to build something better. Let me show you how to construct a robust event-driven foundation that prevents such nightmares.

We start by setting up our project environment. I prefer using modern tooling that supports rapid development and strong typing. Here’s the initial setup that has served me well across multiple production systems.

npm init -y
npm install typescript @types/node eventemitter2 ioredis uuid zod
npm install -D ts-node nodemon jest @types/jest

The TypeScript configuration forms the backbone of our type safety. I always enable strict mode and declaration files – they catch errors during development rather than in production.

{
  "compilerOptions": {
    "target": "ES2020",
    "strict": true,
    "declaration": true,
    "outDir": "./dist"
  }
}

What happens when events lack proper validation? I learned the hard way that type definitions alone aren’t enough. That’s why I integrate Zod for runtime validation, creating a double safety net.

// Event schema definition
const UserRegisteredSchema = z.object({
  userId: z.string().uuid(),
  email: z.string().email(),
  timestamp: z.date()
});

type UserRegistered = z.infer<typeof UserRegisteredSchema>;

The core event bus combines EventEmitter2 with TypeScript generics. This pattern ensures every event handler knows exactly what data to expect. Notice how we maintain type information throughout the event lifecycle.

class EventBus {
  private emitter = new EventEmitter2();

  emit<T>(event: string, payload: T): boolean {
    return this.emitter.emit(event, payload);
  }

  on<T>(event: string, handler: (payload: T) => void): void {
    this.emitter.on(event, handler);
  }
}

Redis Streams provide the durability missing from in-memory event systems. I configure them to store events indefinitely, enabling event replay and audit trails. The combination of in-memory processing with disk persistence gives us both speed and reliability.

// Redis Streams integration
async appendToStream(stream: string, event: DomainEvent) {
  await this.redis.xadd(stream, '*', 
    'event', JSON.stringify(event),
    'timestamp', Date.now()
  );
}

How do you handle events that arrive out of order? I implement version checking and idempotent handlers to maintain consistency. Each event carries a version number that prevents state corruption.

Event handlers become purely functional units that focus on single responsibilities. This separation makes testing straightforward and business logic clear.

// Type-safe event handler
const userRegistrationHandler = async (event: UserRegistered) => {
  const user = await User.create(event.payload);
  await sendWelcomeEmail(user.email);
};

Error handling deserves special attention. I create dead letter queues for failed events and implement retry mechanisms with exponential backoff. This approach maintains system stability while providing visibility into processing issues.

Monitoring event flows proved crucial in production. I add metrics for event throughput, processing latency, and error rates. These indicators help identify bottlenecks before they impact users.

Have you considered how event sourcing could simplify your data model? By storing state changes as events, we can reconstruct any past system state and implement features like time-travel debugging.

Testing event-driven systems requires simulating real-world conditions. I create fixture builders that generate valid test events and mock Redis instances for isolated testing.

// Test event builder
const createTestUserEvent = (overrides?: Partial<UserRegistered>) => ({
  type: 'user.registered',
  payload: {
    userId: '123e4567-e89b-12d3-a456-426614174000',
    email: 'test@example.com',
    ...overrides
  }
});

In production deployments, I scale event processors horizontally and use consumer groups for load distribution. Redis Streams’ built-in consumer groups make this surprisingly straightforward.

The real power emerges when events from different systems combine to create new capabilities. Order processing events might trigger inventory updates and customer notifications simultaneously, all while maintaining data consistency.

This architecture has handled everything from user registrations to financial transactions in my projects. The type safety prevents entire categories of bugs, while Redis ensures no event gets lost.

I’d love to hear about your experiences with event-driven systems. What challenges have you faced, and how did you solve them? Share your thoughts in the comments below, and if this approach resonates with you, please like and share this with others who might benefit from these patterns.