Design a notification system

Intermediate60 minBuilds Notification ServiceRead first: 10.1 Why queues, 10.2 Delivery guarantees and idempotent consumers, 17.1 Timeouts and retries

STEP 1 OF 13

The brief

You are designing the notification service for a large app. Other teams' services call it: "tell user 42 their order shipped", "send this login code", "remind 2 million users about the sale". Your service decides which channels to use (push, email, SMS) based on each user's preferences, sends through third-party providers (APNs, FCM, an email service, an SMS gateway), and tracks what happened.

How big it is

Notification requests from services: 2,000 / second at peak
Reads (status checks, preference lookups): 4,000 / second
Provider rate limit: about 1,000 sends / second per account
p99 goal for accepting a request: under 250 ms

What makes notifications tricky

Providers are slow and flaky. They take 100+ ms, rate-limit you, time out after accepting a message, and occasionally go down.
Duplicates are visible. Two identical login codes or "your order shipped" texts look broken, and SMS costs money.
Not all messages are equal. A login code must arrive in seconds; a marketing email can wait minutes.

All changes saved

0 components · 0 connections

A blank canvas. A better system.

Add components from the palette, then drag between them to connect the request and event flow.

React Flow

Design a notification system

Intermediate60 minBuilds Notification ServiceRead first: 10.1 Why queues, 10.2 Delivery guarantees and idempotent consumers, 17.1 Timeouts and retries

STEP 1 OF 13

The brief

How big it is

Notification requests from services: 2,000 / second at peak
Reads (status checks, preference lookups): 4,000 / second
Provider rate limit: about 1,000 sends / second per account
p99 goal for accepting a request: under 250 ms

What makes notifications tricky

Providers are slow and flaky. They take 100+ ms, rate-limit you, time out after accepting a message, and occasionally go down.
Duplicates are visible. Two identical login codes or "your order shipped" texts look broken, and SMS costs money.
Not all messages are equal. A login code must arrive in seconds; a marketing email can wait minutes.

All changes saved

0 components · 0 connections

A blank canvas. A better system.

Add components from the palette, then drag between them to connect the request and event flow.

React Flow