Publish Subscribe Model

A notification system is responsible for sending alerts to users, such as breaking news, product updates, event reminders, and promotions. Notifications are not limited to mobile push messages. In practice, there are three major notification channels: push notifications, SMS messages, and emails. Defining the Scope and Requirements Before designing a notification system, we must first understand the problem and clarify the system requirements. System design problems are often open-ended, so asking the right questions is essential. Key requirements include: What types of notifications are supported? Is the system real-time? Which devices should receive notifications? What triggers notifications? Can users opt out? What is the expected scale? In our design, the system supports push notifications, SMS, and email. Notifications should be delivered as quickly as possible, with small delays acceptable under heavy load. The system must work across iOS devices, Android devices, and desktop or