HLD-112·Caching & Edge
Easy · 500 ptsGlobal Currency FX Exchange Rate Ticker API
Design a read-intensive currency conversion rate API queried by global e-commerce checkout pages during central-bank rate announcements.
Max p99
≤ 25 ms
Availability
≥ 99.5%
Budget
≤ $2,100
Functional Requirements
- FR-1GET /fx/rates/{pair_code} — Returns latest mid-market and settlement FX rate for a currency pair.
- FR-2POST /fx/rates — Ingests updated market feed ticks from liquidity providers.
- FR-3PATCH & DELETE /fx/rates/{pair_code} — Updates, revokes, or deletes pair_code entries with bounded TTL or explicit cache/index invalidation.
- FR-4Must keep serving sub-25ms FX quotes when backing storage suffers a 5x latency brownout.
Workload Profile
Baseline Quotes20,000 Read RPS / 500 Feed Write RPS
Market Volatility Peak64,500 Read RPS / 1,500 Write RPS
Active Working Set2 GB active spot & historical pair tables
Traffic DistributionHeavy concentration on major pair_code keys (USD/EUR, USD/INR)
Consistency Model
Bounded eventual quote propagation (< 2s) acceptable; published rate ticks must be stored durably.
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