Design an ad exchange that runs a real-time auction across many bidders within a 100ms budget.

When a page loads, an ad slot is auctioned to dozens of bidders and a winner is chosen before the page finishes rendering, all in under 100ms. The design covers the auction mechanism, the brutal latency budget, budget pacing, and fraud. Here is how an exchange runs millions of auctions per second.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.