System Design made easy

Small interactive worlds that show how real systems stay fast. Break one, then fix it.

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A peek inside

A few of the worlds so far, each built around one idea.

The living room at night: a penguin on the sofa watching reels on a giant phone-shaped TV, a cat asleep beside them

Caching

Why the next reel is already waiting. A penguin doomscrolls, and without a cache every swipe means a wait.

 The Krill Grill, a takeaway on a street corner, with penguins queueing at its windows

Load balancing and rate limiting

The Krill Grill at rush hour. One chef drowns in orders while the others stand idle, until someone shares out the work.

 The Emperor hotel: a lobby with a front desk and a queue, and the kitchen, office, linen room and store behind

Reverse proxy

The Emperor hotel. Guests barge into the back of house, until a front desk answers for every room.

 Floe Pops, an ice lolly factory: a pump filling moulds on the freezer's roof, a conveyor belt of lollies, a spill by the freezer, a wrapping machine, a forklift loading a truck, and a penguin asleep at the control desk

Backpressure and batching

Floe Pops, an ice lolly factory. The freezer outruns the wrapper until the spill shorts out the power, and someone has to watch the belt and press stop.

 The Iceberg Express, a post office: a counter with a queue and an ENQUIRIES window, brass pneumatic tubes over the pigeonholes, a sorting room with a stock rack under an ORDERS TODAY screen and a ledger screen, and a snowy street of front doors outside

Idempotency

The Iceberg Express post office. Its tubes lose orders and receipts, and the clerk can't tell which went missing. Send it again, and customers get charged twice, until every order carries a tracking number.

 Pebble Bay's border crossing: travellers queue under a welcome arch to a guard's booth and barrier, a row of igloo records offices with screens, and a big screen on the ice cliff showing the ring of letters

Sharding and consistent hashing

Pebble Bay's border records. Travellers' files are kept in igloo offices by first letter, and nearly everyone's name starts with P, so one office is mobbed until it caves in. Hashing spreads the files, and a ring stops a new office moving everyone's records.

Watch it break, then fix it

Each world opens on the problem. Flip the switch to add the fix, and the penguins show you what changed.

A short panel beside each world explains the real system underneath in plain English, with a few real numbers and links to go deeper.

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