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.