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Design a notification system

Skeleton Summary​

Step 1

  • Ask questions on types of notifications, whether it's real-time, supported devices, notifications triggered by what, user opt-out feature, and how many notifications a day.

Step 2: High-level design

  • Different types of notifications: iOS uses APNS (Apple Push Notification Service), Android uses FCM (Firebase Cloud Messaging), SMS uses SMS services like Twilio/Nexmo, and email uses commercial email services like Sendgrid/Mailchimp.
  • Flow 1: Contact info gathering flow: store phone numbers and email addresses in the user table and mobile device token in the device_token table in the database.
  • Flow 2: Notification sending/receiving flow. (High-level design diagram). Identify problems and propose solutions:
    • Problem: SPOF (single point of failure) if there's only one notification server. -> Solution: Have multiple notification servers and set up automatic horizontal scaling.
    • Message Queue
    • Cache between DB and Notification services

Step 3: Design deep dive

  • Reliability:
    • Persist notification data in a database and implement a retry mechanism to prevent the notification system from losing any data.
    • Introduce a dedupe mechanism to handle duplicate notifications in a distributed environment.
  • Additional components and considerations: notification template, notification settings, rate limiting, retry mechanism, security in push notifications, monitor queued notifications, and event tracking.