Building a scalable system that sends out millions of notifications.

Requirements:

• 10 million push notifications daily to different devices
• A soft real-time system. We want a user to receive notifications as soon as possible. If the system is under a high workload, a slight delay is acceptable.
• Notifications can be triggered by client applications
• User can opt-out (unsubscribe)

Source: ByteByteGo https://medium.com/@meenak1996/system-design-of-notification-system-8c2828be3e8e

Source: ByteByteGo https://bytebytego.com/guides/how-does-a-typical-push-notification-system-work/

Third-party Communication APIs

• iOS: Apple Push Notification Service (APNS)
• Android: Firebase Cloud Messaging (FCM)
  • Jpush, PushY are used in China
• SMS: Twilio, Nexmo
• Email: Sendgrid, Mailchimp

Notification Servers

Missions

• Provide internal APIs for business logic services (e.g., payment service)
• Verify emails, phone numbers, etc.
• Query the database or cache in order to render a notification content (e.g., HTML).
• Put notification data to message queues for parallel processing. The data includes:
  • metadata (user ID, even ID, notification type, payload, timestamp, etc)
  • filled template