Design 1 - The News Feed

"Design a social feed: users follow each other, post updates, and see a feed of recent posts from accounts they follow."

1. Requirements and Numbers

Pause. Ask your clarifying questions and run the arithmetic before reading.

Clarify the user count, feed order, follower distribution, and freshness requirement; assume 100M daily active users and begin with a chronological feed, leaving ranking as a follow-up. The median user follows 200 accounts, while celebrities may have 50M followers; require each post to appear in follower feeds within approximately 10 seconds