Design a scalable image-based social network

Design the backend system for a social networking website primarily focused on sharing images (similar in spirit to an image-centric social app). Users should be able to: - Sign up, log in, and manage a profile. - Upload images (with optional captions). - Follow/unfollow other users. - View a **feed** of images posted by accounts they follow. - Like and comment on images. The interviewer specifically cares about how your design will handle **foreseeable, large-scale user growth**: potentially tens of millions of users, high write traffic for uploads and interactions, and very high read traffic for feeds. **Tasks** 1. Clarify and state the key **functional** and **non-functional** requirements (e.g., latency, availability, consistency, durability). 2. Propose a **high-level architecture**, including major components/services (e.g., API gateway, user service, post/media service, feed service, databases, cache, object storage, CDN). 3. Design how **image upload and retrieval** works end-to-end. 4. Design how a user's **home feed** is generated and served efficiently at scale. 5. Explain how you will **scale the system** as the number of users and operations increases, including: - Horizontal scaling of stateless services. - Database sharding/replication strategies. - Caching and CDN usage. - Asynchronous processing and message queues. 6. Discuss key **trade-offs** (e.g., push vs. pull feed generation, consistency vs. latency) and how your choices handle high load and growth. You can assume a cloud environment (object storage, managed databases, load balancers, etc.) is available.