Learn

Short lessons on the mechanisms a design is judged by. Each one ends on the canvas, with something to fix rather than something to agree with — and then hands you the task it was about. Nothing is scored and nothing is locked.

• 01starter4 cardsA box on its own does nothingThe first habit to unlearn: drawing the right component is not the same as meeting the requirement.load balancerservicehealth checksfailoverstatelessness
• 02middling4 cardsOne address, three services behind itWhat a reverse proxy in front of several backends is actually for — and the thing people expect from it that it does not do.api gatewayservicemobile clientone entry pointrouting by pathrate limits in one place
• 03middling4 cardsNobody waits five minutesThe difference between a call you wait for and work you hand over — and why one of them is the reason a queue is on almost every diagram in the pool.queueworkerserviceexternal apisync and asynchanding work overredelivery
• 04middling3 cardsIt will arrive twiceA queue promises the job is not lost. It does not promise the job happens once — and the difference is somebody being charged twice.queueworkerservicesql databaseat-least-onceduplicatesidempotency
• 05hard2 cardsThe numbers have to fit each otherTwo properties can each look sensible and still be impossible together. This is the arithmetic that catches it, and where the trainer does it for you.workerexternal apiqueuerate limitsconcurrencycapacity arithmetic

More are coming. The order is a suggestion and the difficulty is a label — nothing has to be finished before anything else is opened.