# Design a News Feed — System Design

Source: https://www.geekswithgeeks.com/en/system-design/sd-design-news-feed

> Fan-out strategies for showing followed content, ranked, fast.

## Requirements

Users follow others and post updates; opening the app shows a ranked feed of recent posts from people you follow. Assume most users follow hundreds, some celebrities have tens of millions of followers.

## Push (fan-out on write)

When a user posts, immediately write that post into every follower's precomputed feed (a list in Redis). Reading the feed is then one fast lookup. Great for typical users — terrible for a celebrity with 50M followers (one post = 50M writes).

## Hybrid: push for most, pull for celebrities

Like a newspaper delivering to most houses (push) but leaving today's front page at newsstands for a few very popular columnists (pull) — most systems push to normal followers' precomputed feeds and, at read time, merge in a live pull of any celebrity accounts the user follows.

## Ranking is a separate concern

Fan-out solves delivery; a separate ranking service (recency, engagement prediction) reorders the candidate posts at read time. Keep the storage/delivery pipeline dumb and fast, and ranking pluggable.