System Design Interview

Wrap Up

Wrap up 1 min readLesson 4 of 4

Notifications are indispensable because they keep us posted with important information. It could be a push notification about your favorite movie on Netflix, an email about discounts on new products, or a message about your online shopping payment confirmation.

In this chapter, we described the design of a scalable notification system that supports multiple notification formats: push notification, SMS message, and email. We adopted message queues to decouple system components.

Besides the high-level design, we dug deep into more components and optimizations.

  • Reliability: We proposed a robust retry mechanism to minimize the failure rate.

  • Security: AppKey/appSecret pair is used to ensure only verified clients can send notifications.

  • Tracking and monitoring: These are implemented in any stage of a notification flow to capture important stats.

  • Respect user settings: Users may opt-out of receiving notifications. Our system checks user settings first before sending notifications.

  • Rate limiting: Users will appreciate a frequency capping on the number of notifications they receive.

Congratulations on getting this far! Now give yourself a pat on the back. Good job!

Reference materials

  1. Twilio SMS: https://www.twilio.com/sms
  2. Nexmo SMS: https://www.nexmo.com/products/sms
  3. Sendgrid: https://sendgrid.com/
  4. Mailchimp: https://mailchimp.com/
  5. You Cannot Have Exactly-Once Delivery: https://bravenewgeek.com/you-cannot-have-exactly-once-delivery/
  6. Security in Push Notifications: https://cloud.ibm.com/docs/event-notifications?topic=event-notifications-en-push-apns
  7. Key metrics for RabbitMQ monitoring: https://www.datadoghq.com/blog/rabbitmq-monitoring/

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