Design an e-commerce category page

Quick Overview

Design an e-commerce category page evaluates requirements, scale assumptions, API/data design, architecture, trade-offs, failure modes, and rollout in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Design an e-commerce category page

Company: Instacart

Role: Software Engineer

Category: System Design

Difficulty: hard

Interview Round: Onsite

Design the backend and serving architecture for an e-commerce category page (e.g., /electronics/phones) with faceted filtering (brand, price, rating), sort options (relevance, price, popularity), pagination/infinite scroll, SEO-friendly rendering, caching for high-traffic categories, optional personalization, and near-real-time inventory/price updates. Specify APIs, data models, indexing/search strategy, ranking signals, cache hierarchy (CDN/edge/app cache), read/write patterns, consistency vs. freshness strategy, scaling to 10^6+ SKUs and 10^4 QPS, and approaches for A/B testing, metrics, and monitoring. Discuss key trade-offs and bottlenecks.

Quick Answer: Design an e-commerce category page evaluates requirements, scale assumptions, API/data design, architecture, trade-offs, failure modes, and rollout in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

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Jul 15, 2025, 12:00 AM
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Design an e-commerce category page

System Design: Category Page with Facets, Sorting, Pagination, SEO, Caching, Personalization, and Real-Time Updates

Design the backend and serving architecture for an e-commerce category page (e.g., /electronics/phones) that supports:

Functional Requirements

  • Faceted filtering: brand, price, rating (extensible to others like attributes, availability)
  • Sorting: relevance, price (asc/desc), popularity
  • Pagination and infinite scroll (cursor-based preferred)
  • SEO-friendly rendering (SSR/SSG, crawlability, canonical URLs)
  • Optional personalization of ranking
  • Near-real-time inventory and price updates

Non-Functional Constraints

  • Scale: 10^6+ SKUs, 10^4 QPS on category endpoints
  • High-traffic categories should benefit from aggressive caching (CDN/edge/app)
  • Specify consistency vs freshness strategy
  • Specify APIs, data models, indexing/search strategy, ranking signals
  • Specify cache hierarchy and keys, read/write patterns
  • Approaches for A/B testing, metrics, and monitoring
  • Discuss key trade-offs and likely bottlenecks

Clarifying Questions to Ask Guidance

  • Clarify users, core use cases, read/write patterns, scale, latency, availability, and data retention.
  • State explicit assumptions before making sizing or architecture decisions.
  • Prioritize the functional path first, then address reliability, security, observability, and rollout.

What a Strong Answer Covers Guidance

  • A scoped requirements summary with concrete non-goals and success metrics.
  • API, data model, architecture, consistency, capacity, and operations.
  • Reasoned trade-offs among simple and scalable designs, including bottlenecks and failure modes.
  • A validation, monitoring, migration, and launch plan appropriate for the risk level.

Follow-up Questions Guidance

  • What breaks first at 10x traffic or data volume?
  • How would you degrade gracefully during dependency failures?
  • What metrics and alerts would prove the design is healthy after launch?

Submit Your Answer to Earn 20XP

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