Design a Stock Price Movement Alert System

Published 3 October 2026

HLD Round — Stock Price Movement Alert System

The high-level design round asked me to build a stock-price alerting service. The system received fresh stock prices from an exchange roughly once per second, while users could configure alerts that triggered when a stock moved by a specified percentage over a chosen rolling window. Supported windows ranged from minutes through years and were continuously rolling relative to the current timestamp rather than aligned to calendar boundaries. A subscription disappeared after triggering once or after remaining untriggered for one month. The interviewer focused on comparing alternative designs and discussing non-functional requirements such as storage usage and notification latency.