System design interview question
"Design a coupon system for a large e-commerce site. Marketing creates campaigns with rules — 20% off electronics over ₹2,000, first order only, one per customer, 10,000 total redemptions. The code is validated at checkout and applied to the order. It must be impossible to over-redeem or stack coupons in ways we did not intend."
a rules engine plus a hard redemption limit under concurrency — and, more subtly, that promotions are an adversarial domain where users actively share and abuse codes. The distinguishing content is: expressing arbitrary business rules without deploying code, enforcing global caps atomically, and preventing the classic "apply coupon twice" race.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
Book a free mock interviewAll 132 system design interview questions
System design mock interviews · DSA interview questions · Free mock interview practice · Browse interviewers · Sign in