Implement Pub/Sub System

Publisher/Subscriber System Design:

1. Core Components:

   • Message Broker
   • Topic Manager
   • Subscriber Manager
   • Message Queue

2. Implementation:

interface Publisher {
  publish(topic: string, message: Message): void;
}

interface Subscriber {
  subscribe(topic: string): void;
  unsubscribe(topic: string): void;
  receive(message: Message): void;
}

class MessageBroker {
  private topics: Map<string, Set<Subscriber>>;
  private messageQueue: Queue<Message>;

  async publish(topic: string, message: Message): Promise<void> {
    const subscribers = this.topics.get(topic);
    for (const subscriber of subscribers) {
      await this.deliverMessage(subscriber, message);
    }
  }

  private async deliverMessage(subscriber: Subscriber, message: Message): Promise<void> {
    try {
      await subscriber.receive(message);
    } catch (error) {
      await this.handleDeliveryFailure(subscriber, message);
    }
  }
}

3. Features:

   • Message persistence
   • At-least-once delivery
   • Dead letter queue
   • Message ordering
   • Back-pressure handling

4. Scalability:

   • Partitioned topics
   • Consumer groups
   • Load balancing
   • Fault tolerance

Company Context (Netflix):

• High availability
• Eventual consistency
• Failure recovery
• Performance monitoring