Why admission control
When demand exceeds capacity, you can either drop requests randomly or shape them into a queue and admit at a controlled rate. A virtual waiting room turns a stampede into an orderly line.
How it works
- Arriving buyers receive a position token and wait outside the protected system.
- A scheduler releases tokens at the rate the checkout system can absorb.
- Released buyers get a short access window to complete checkout before their slot is reclaimed.
Fairness and abuse
- First in first out feels fair but invites bots; add light verification.
- Cap the window so an idle admitted user does not block the line.
- Make position tokens single use so they cannot be shared.
Key idea
Admission control shapes excess demand into a queue and releases buyers at a rate the backend can absorb, trading wait time for stability and fairness.