Build it: Failover
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 web app needs a database tier. Writes go to a primary. Reads can come from replicas. Build it. Press Play. Then <strong>kill the primary</strong> with the red X. The system should keep serving reads even though writes are now stuck. That is a failover-ready design.