Build a home-feed service from parts, press Run, and see whether it saves posts, opens feeds and delivers every new post to the followers, and whether it keeps doing so when a server, the feed cache or the fan-out worker dies.
Visual challengeDesign a home feed (a news feed)
Names
Components
Drag onto the board, or tap to add.
Traffic
Compute
Data
Messaging
Press enter or space to select a node. You can then use the arrow keys to move the node around. Press delete to remove it and escape to cancel.
Press enter or space to select an edge. You can then press delete to remove it or escape to cancel.
Settings hover or tap a component, then its iconLink drag from any dot to another componentRemove select it, press DeleteBreak Break it in a part's settings arms it; it fails when you press Run tests
Link color = the component it leaves:Entry pointsTraffic routingServersStoragedown, unlinked or overloaded
A simplified model, not a real cloud. Times are in model milliseconds, the feed cache is always warm, and prices are made up to compare designs. About 1 request in 50 is a post (chapter 21.1) and sends one job to the queue, but every job weighs the same, so the board cannot show one account with millions of followers (the celebrity problem), a cache that restarts empty, or ranking.