Think of a notification engine as a smart postman. It delivers messages to users through email, SMS, or push notifications, based on their preferences and specific triggers.
Designing a good notification system teaches you the basics of building scalable and reliable systems.
What You’ll Learn in This System Design Module
In this module, we will cover how to design a complete notification engine from scratch, including:
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The end-to-end architecture of a notification system
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Supporting different types of notifications
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Real-time logging and monitoring
Applying core design patterns for clean and flexible design
Example: Zomato
When you order food on Zomato, you might get a message saying, “Your order is out for delivery.” The notification engine decides:
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What message to send
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When to send it
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Which channel to use (email, SMS, or app notification)
This is the job of a notification engine: delivering the right information to the right user at the right time.
Multiple Notification Types
A good notification engine can handle messages across different channels:
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Email – For example, Netflix might send a renewal reminder.
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SMS – Banks often use SMS for OTPs or account activity alerts.
Push Notifications – Social apps use these to instantly grab your attention.
Real-Time Logging
Every message sent is tracked, just like checking the status of a delivery.
If an OTP or notification fails, the log helps teams quickly find the problem and fix it.
UML Diagram
Design Patterns in Action
A strong notification system doesn’t start from scratch every time. It uses proven design patterns to make the system flexible and easy to maintain:
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Observer Pattern – When an event happens, like an order status changing, all relevant services (SMS, email, push) are notified automatically.
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Strategy Pattern – The system chooses how to deliver the notification at runtime, for example, picking between email or SMS.
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Decorator Pattern – Extra behaviors, such as marking a message as “high priority” or retrying on failure, can be added without changing the main logic.
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Singleton Pattern – Only one notification manager exists, serving as the central point of control for the whole system.
Summary
A notification engine is like a smart postman that delivers messages to users via email, SMS, or push notifications based on triggers and preferences. It ensures the right message reaches the right user at the right time, while tracking delivery and failures in real time. A well-designed system uses design patterns: Observer notifies relevant channels when events happen, Strategy chooses how to send messages, Decorator adds extra features like retries or priority, and Singleton provides a central manager. This makes the engine flexible, reliable, and easy to maintain, even at large scale.