←SYSTEM DESIGNDesign a Payment Gateway (Stripe)StripeSquare
TRAFFIC LEVEL—/3
CONSTRAINTS
Consistency modelStrong (ACID required)
Double-charge rateMust be 0%
Retry safetyAll endpoints idempotent
Availability target99.999% (5.26 min/yr downtime)
Audit requirementEvery state change logged
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
StripeSquare
Architect a B2B payment API. It must strictly guarantee 100% data consistency, no dropped payments, and absolute protection against double-charging due to network retries.