System Design - Push Notification System for New Posts

System Design - Push Notification System for New Posts

You are tasked with designing a notification system that sends push notifications to followers when an author publishes a new post. The system should handle the following requirements:

1. Followers and Devices: Followers may have multiple devices, and the system should support sending notifications to all of their devices.
2. Notification Preferences: Followers can mute or disable notifications. The system should respect these preferences.
3. Authors and Posts: Some authors may have a large number of followers, and the system should efficiently handle the notification process for these authors.
4. Scalability: The system should be scalable to handle a large number of users, devices, and notifications.

Examples:

• User A follows User B and User C.
• User B publishes a new post.
• User A should receive a push notification on all their devices, unless they have muted or disabled notifications for User B.

Constraints:

• The system should be able to handle a high volume of notifications in a short period.
• The system should minimize the latency between a post being published and the notification being sent.
• The system should be fault-tolerant and handle failures gracefully.

Hints:

• Consider using a publish/subscribe model for efficient notification delivery.
• Use caching to store user preferences and device information.
• Implement rate limiting to prevent abuse and ensure system stability.

Solution:

1. Data Model:

   • User: Contains user information, including their device tokens and notification preferences.
   • Post: Contains post information, including the author and publication date.
   • Follower: Represents the relationship between a user and an author they follow.

2. Notification Service:

   • When a post is published, the notification service is triggered.
   • The service queries the follower table to find all users following the author of the post.
   • For each user, the service checks their notification preferences and device tokens.
   • If a user has not muted or disabled notifications, the service sends a push notification to all their devices.

3. Scalability:

   • Use a message queue to handle the high volume of notifications and ensure they are processed in order.
   • Implement sharding to distribute the load across multiple database instances.
   • Use a caching layer to store user preferences and device tokens for fast access.

4. Fault Tolerance:

   • Implement retries for failed notifications with exponential backoff.
   • Monitor the system for failures and alert the team if issues arise.
   • Use a distributed database to ensure data is replicated and can be recovered in case of a failure.

By following these guidelines, you can design a robust and scalable push notification system for new posts that meets the requirements outlined in the problem statement.