Project: a news feed
Lantern Clubs asks you to design its home feed. The fictional workload has 200,000 daily readers, 12 pages per reader, an eightfold peak and one broadcaster with 2,000,000 followers. Deliver a checked requirements sheet, peak estimate, cursor API, inbox table and delivery board. A deleted post must stay hidden even if its inbox entry remains.
You are designing a feed for Lantern Clubs, a fictional community app. Most members follow a few hundred people. One broadcaster has two million followers, so pushing every post into every follower feed can dominate the write tier. Reading every followed account on each request has the opposite cost.
Build a hybrid that makes this distinction explicit. Ordinary posts can fan out to stored inboxes; a large broadcaster can be merged into the feed during reads. Keep post content authoritative so a deleted post doesn't remain visible merely because an old inbox entry survives. You'll carry the same board through requirements, estimates, API, model and delivery decisions. The final recommendation must fit both ordinary members and the broadcaster.
Ordinary author -> queued fan-out -> feed inbox
Broadcaster -> merge recent posts on read
Build a feed that handles both ordinary members and a large broadcaster.