System Design: Newsfeed System

What is a newsfeed?

A newsfeed is an ordered collection of content selected for a user. This exercise draws candidates from friends, followed accounts, pages, and groups, with the user’s own posts included where the product requires them. Posts may contain text, images, or video. Ads and recommendations outside those relationships are optional additional candidate sources, not inherent parts of every feed.

The engineering problem is to combine candidate retrieval, eligibility checks, ranking, and delivery within a response budget. Content and relationships change while users scroll, so the design also needs rules for freshness, deletion, and stable pagination.

This lesson will discuss the high-level and detailed design of a newsfeed system for a social platform such as Facebook, Twitter, or Instagram.