Build it: Circuit Breaker
An interactive sandbox where you drag real components together, connect them, and run a live traffic simulation to see where the design breaks.
Challenge: Your app calls a flaky downstream service. Without protection, slow calls pile up your threads. Place a circuit breaker (a rate limiter stands in for it) between them. Also place a fallback cache for when the breaker is open. Then kill the downstream with the red X. The breaker should "trip" and the app should serve from the cache.