Uber System Design Interview: Stock Price Move Alerts

The interviewer opens

Hi, and thanks for joining. Welcome to your interview for the software engineer role at Uber. We'll design a system together, with you sketching on the whiteboard on the right as you talk, and you can pause anytime with the Pause button at the top right if you need a break.

The problem is in the Problem tab: it's a stock price move alert system, a real-time notification pipeline of the kind that matters at Uber's scale. Please read through the requirements and ask me anything you'd like clarified before you start drawing.

The problem

Design a system that consumes a live stream of stock prices (symbol, current price, previous close) and sends a push notification to every user subscribed to a stock when its price moves more than 5% from the previous close.

Must do

• Users subscribe to and unsubscribe from stocks
• Consume a continuous feed of price ticks: symbol, current price, previous close
• Detect when a stock moves more than 5% up or down from its previous close
• Send a push notification to every subscriber of that stock

Must hold

• A user must not receive the same alert twice
• Alerts must reach subscribers promptly after a move