6. Design a News Feed

The brief

Design a following-based news feed, starting with reverse chronological order. Follow publication through feed reads and pagination, including a high-fan-out author. Explain how deletion and privacy changes affect precomputed entries before discussing an optional ranked feed.

• There are 10 million daily active users, each opening their feed 20 times/day.
• Publish 20 million posts/day; a few authors have over 5 million followers.
• Users follow and unfollow authors. Authors can delete posts or make their account private.

Constraints

Feed latency≤ 300 milliseconds

Declare p95 server latency for a page of 20 entries.

Visibility enforcement

Do not expose a deleted or unauthorized post solely because a feed entry was precomputed.

Pagination contract

Explain duplicates and omissions when new posts arrive between page requests.

What to cover

1. 01

   Data and API

   Define posts, follows, feed entries and cursors.

2. 02

   Publication and feed assembly

   Show push, pull or hybrid responsibilities and high-fan-out handling.

3. 03

   Capacity estimates

   Estimate feed-read QPS and fan-out work with explicit follow-count assumptions.

4. 04

   Freshness and privacy walkthrough

   Trace a backlog and a privacy change, comparing latency, freshness and write amplification.

Worked designs

Explore the architecture and decisions, then build on an example with Coach.

Official design

Design a News Feed like Facebook

A home feed for 2 billion users: fan-out on read, on write, and the hybrid for huge accounts, with precomputed feeds, cursors and hot posts: one-hour boards for junior, senior and staff, with the theory behind them.

Explore the design

Review rubric

AI feedback uses these criteria. Scores are practice feedback.