Design a scalable Instagram-like platform
Overview
This question evaluates a candidate's ability to design a scalable, read-heavy social media backend encompassing media ingestion and storage, personalized feed generation, data modeling, sharding, consistency vs availability trade-offs, observability, and cost/DR planning, testing competencies in distributed systems, performance engineering, and operational design. Commonly asked in system design interviews to assess architectural reasoning and trade-off analysis, it is categorized under System Design and requires both high-level conceptual thinking and practical application details such as APIs, data models, capacity estimates, and component-level considerations.
Design: Instagram-like Photo/Video Sharing Platform (Technical Screen)
Context
Design a photo/video sharing platform with core social features and a personalized feed. Optimize for large-scale read-heavy workloads and mobile clients. Optional features (stories, DMs) may be stubbed but need not be fully designed.
Requirements
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Core features
- User sign-up/login, follow/unfollow
- Upload photos/videos
- Personalized home feed
- Likes, comments
- Notifications
- Search (users, hashtags, captions)
- Optional: stories, direct messages (outline only)
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Deliverables
- Public APIs (CRUD and feed endpoints)
- Data models and key indexes
- High-level architecture and components
- Media ingestion pipeline: upload, storage, thumbnailing/transcoding, CDN delivery
- Feed generation and ranking: pull vs push, fan-out strategies, timelines, caching, handling hot accounts
- Consistency vs availability trade-offs
- Sharding/partitioning strategy and read/write scaling
- Privacy and access control
- Abuse/spam mitigation
- Observability (metrics, logging, tracing)
- Cost controls
- Multi-region disaster recovery
- Back-of-the-envelope capacity estimates
- Evolution plan from MVP to planet scale
Solution
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