System Design: Instagram-like Photo and Short-Video Platform

Goal

Design an Instagram-like platform for photos and short videos. The design should cover product features, scale assumptions, APIs, storage, feed/ranking, media handling, and operational concerns.

Functional Requirements

• Post: create, edit (caption), delete; single image or short video; hashtags, mentions, location
• Follow graph: follow/unfollow; follower and following lists
• Interactions: like/unlike, comment/delete, counts
• Feed: home timeline combining followed accounts and recommendations; infinite scroll; pagination
• Notifications: likes, comments, follows, mentions; push and in-app
• Profiles: public/private accounts; block/mute; profile media grid

Non-Functional Goals

• Availability: high availability across regions for read path (feed/media). State explicit SLOs.
• Latency: sub-200 ms p95 for metadata APIs; smooth media playback
• Scalability: support 100M+ DAU; elastic fan-out; hot accounts handling
• Consistency: read-your-writes for own actions; eventual for others; clear timeline semantics

Deliverables

1. APIs (CRUD for posts, follow, like, comment, feed, notifications)
2. Data model and storage choices
3. Media handling: upload, transcode, storage, CDN
4. Feed generation and ranking pipeline
5. Timeline consistency model
6. Caching and search
7. Sharding/partitioning and replication
8. Background jobs (fan-out, media processing)
9. Rate limiting and abuse prevention
10. Privacy/permissions model
11. Observability (metrics, logs, traces), disaster recovery
12. Back-of-the-envelope capacity: QPS, storage, bandwidth, and rough cost

Estimation

• State reasonable scale assumptions (e.g., MAU/DAU, posts/day, follower distribution) and compute QPS, storage, and bandwidth.
• Justify any additional assumptions you make.