Flash Sale

01What exactly is being sold — units with identity, or just a count?

N identical units against one capacity counter — no seat map, no per-unit identity. Sold out means the counter reached zero, nothing else.

02A million people are staring at the product page — what do they see?

A fully static page (image, price, countdown, stock badge) served from the CDN edge — browsing generates zero reads on application servers.

03What happens the moment someone taps Buy?

An admitted buyer either reserves exactly one unit and gets a short payment window, or gets an instant, unambiguous sold-out answer — never a spinner or a 500.

04And the people we cannot serve yet?

Everyone over capacity waits in a virtual waiting room with a live position or wait estimate — admission is controlled, so nobody’s request dies in a timeout.

05Can one person buy five?

One unit per account (and per payment method), enforced in the same atomic step as the decrement so a racing bot cannot slip past the cap.

06A buyer reserves a unit and their card declines — is that unit gone?

A reservation holds the unit for a few minutes; if payment does not complete, the hold expires and the unit returns to the pool for the next buyer.

01What is the hard line on inventory?

Zero oversell, ever: check-and-decrement is one atomic operation and the counter can never go below zero — this is the invariant everything else serves.

02What do the 990,000 losers experience?

A fast, honest answer for the 99% who lose: sold-out responses return in well under a second, because a clear no beats a hopeful timeout.

031000x in seconds — can autoscaling absorb that?

The sale instant is announced, so capacity is pre-scaled and caches pre-warmed before it — reactive autoscaling measures the spike after it has already fallen over.

04Bots will script this — what is the fairness bar?

A scripted client gains no edge: buying requires an admission token from the waiting room, and admission order is randomized within a window rather than raw first-click.

05How do we know we sold exactly the stock we had?

Post-sale reconciliation proves counter decrements equal confirmed orders plus expired holds — drift under retries is found and repaired, not assumed away.