HLD-127·Caching & Edge
Easy · 500 ptsE-Commerce Promo Code & Eligibility Rule Validator
Design a checkout promo-code eligibility service validating campaign rules, minimum cart thresholds, and merchant promo metadata during seasonal sales.
Max p99
≤ 38 ms
Availability
≥ 99.5%
Budget
≤ $2,500
Functional Requirements
- FR-1GET /promos/{promo_code}/validate — Evaluates campaign dates, cart eligibility, and discount rules.
- FR-2POST /promos — Publishes or pauses merchant promotional codes and logs redemptions.
- FR-3PATCH & DELETE /promos/{promo_code}/validate — Updates, revokes, or deletes promo_code entries with bounded TTL or explicit cache/index invalidation.
- FR-4Must sustain sub-40ms p99 cart checks during influencer promo drops and DB node failure.
Workload Profile
Baseline Cart Checks20,000 Read RPS / 1,800 Redemption Write RPS
Influencer Code Drop58,000 Read RPS / 5,000 Write RPS
Active Working Set8 GB active promo campaigns & eligibility rules
Traffic DistributionExtreme hot-key skew on viral promo_code strings
Consistency Model
Eventual campaign pause propagation (< 3s) for unlimited-use sitewide promo codes.
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