News feed. Fan-out on write and the hybrid

A social network feed for 5 million DAU: ready-made timelines in a cache, fan-out through a queue, and when celebrities arrive, a hybrid that also saves money.

Diagram of a news feed: a post fans out through a queue into ready timelines in a cache, while celebrity posts are pulled in at read time, a hybrid.

System Design — Load balancers, caches, queues and regions: build a system that holds the load