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).