←SYSTEM DESIGNDesign a Flash Sale SystemAmazonShopifyAlibaba
TRAFFIC LEVEL—/3
CONSTRAINTS
Inventory1,000 units
Concurrent users500,000
Request spike500k requests in first 5 sec
Oversell toleranceZero — must not sell > 1,000
Site availabilityMust stay up under 500k RPS
Compute & Network
Load BalancerDistribute traffic
API GatewayEntry point / auth
API ServerBusiness logic
Worker NodeAsync processing
CDN EdgeGlobal cache
WebSocket GatewayPersistent connections
Data Stores
PostgreSQLRelational DB
MySQLRelational DB
CassandraWide-Column DB
DynamoDBNoSQL / Managed
S3 BucketObject storage
Queues & Cache
Redis CacheIn-memory store
KafkaEvent stream
ZookeeperCoordination
Specialized
Bloom FilterProbabilistic set
Rate LimiterThrottling
Geohash ServiceGeospatial index
Trie ServerPrefix search
APNS / FCMPush notifications
AggregatorBatch / roll-up
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🚨 INCIDENT
AmazonShopifyAlibaba
Design a flash sale system: 1000 PS5 consoles go on sale at exactly 9:00 AM. 500,000 users rush the site simultaneously. Exactly 1000 units must be sold — no overselling, no duplicate orders, and the site must remain responsive under the load spike.