37. Design a News Feed
1
The interview prompt2
37.1 What do you ask first?3
37.2 How big is this, really?4
37.3 What are the doors?5
37.4 What do we store?6
37.5 What does the whole system look like?7
37.6 Fan-out on write or on read?8
37.7 How do you solve the celebrity problem?9
37.8 How does ranking work?10
37.9 How do the feed cache and pagination work?11
37.10 What would you say in the last five minutes?12
Score yourself13
Variations to practise14
Sources15
Code lab37. Design a News Feed
The interview prompt
3 min read+10 XP
This chapter is a full interview round, played out step by step. The interviewer's lines are in quotes. At each step you'll see what a strong candidate says, the pushback the interviewer throws, and how to answer it. At the end, grade yourself with the rubric.
How to use this chapter
- Read only the prompt below. Then stop.
- Set a 45-minute timer and do the whole round yourself, on paper or a whiteboard, out loud. Use the framework from Chapter 1: READ, then Draw, Dive, Defend.
- Then read the walkthrough and compare. Score yourself with the rubric at the end.
Chapter 23 introduced fan-out with the bookstore's "authors you follow" feed. This round is the full-size version: the home feed of a large social app, where reads, writes and ranking all matter at once.
The prompt
"Design the home feed for a social app, like Instagram's or X's. Users follow other users and see their posts in a feed when they open the app."
Stop here. Start your timer.