Build it: Pub/Sub
An interactive sandbox where you drag real components together, connect them, and run a live traffic simulation to see where the design breaks.
Challenge: A signup service publishes a <strong>user.signed_up</strong> event 30 times per second. Several other services need to react. Email. Analytics. CRM. Recommendations. Build the fan-out. Add a <strong>topic</strong> with multiple <strong>subscribers</strong> behind it.