Design an e-commerce price tracking service

Design a backend system similar to popular price-tracking sites that monitor product prices on large e-commerce platforms (for example, a site that tracks prices on a major online retailer and notifies users when prices drop). ### Functional requirements - Users can search for a product (by URL or product ID) and start tracking its price. - The system periodically fetches the latest prices for tracked products from the e-commerce site (via API or web scraping, depending on assumptions). - For each product, the system stores a **price history** (timestamped prices) that users can view as a chart or table. - Users can create **alerts** with conditions like: "notify me when the price goes below X" or "notify me when there is at least a Y% drop from the highest price." - When an alert condition is met, the system sends notifications (email, push, etc.). ### Non-functional requirements - Support tracking **tens of millions of products** and **millions of users**. - Prices should be reasonably fresh (e.g., updated every 15–60 minutes for popular products, less frequently for long-tail items). - The system should be **highly available**; temporary delay in price updates is acceptable, but losing data or sending duplicate alerts should be minimized. - The system should be **cost-efficient**, given the large volume of historical price data. ### Key points to cover - Clarify any assumptions you need (data source: API vs scraping, exact freshness targets, regions, etc.). - Propose: - Overall **high-level architecture and major components**. - **Data model** for products, price history, user subscriptions, and alerts. - Approach to **fetching and updating prices** at scale. - How you will implement and scale **alert evaluation and notification**. - Discuss trade-offs around **storage**, **crawling frequency**, **consistency**, **fault tolerance**, and **cost**. - Be prepared to go into deeper design details on one or two critical parts (for example, the price ingestion pipeline or the alerting system).