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SYSTEM DESIGNDesign a Global Chat App (WhatsApp)MetaDiscord
TRAFFIC LEVEL
—/3
CONSTRAINTS
Total users1 Billion
Daily active users500 Million
Messages per day100 Billion
Avg message size100 bytes
Storage per day~10 TB
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
MetaDiscord

Design 1-on-1 messaging for 1 billion users. Messages must be delivered in real-time, and read receipts must be supported.

📥 Assigned to:You — Senior Engineer
SCALE LEVELS
1
10,000 RPS
Target: <800ms
2
100,000 RPS
Target: <500ms
3
1,000,000 RPS
Target: <80ms
GLOBAL SUCCESS RATE
100.0%
P99 LATENCY
45ms
Target: < 200ms
TOTAL RPS INGESTED0 / 11,000
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