05

Level 5 of 5

Battleground

This is what a FAANG staff-level interview actually looks like. Two billion users, zero tolerance for message loss, ordering guarantees under partition, and failure scenarios that don't have clean answers.

BATTLEGROUND
WhatsApp
Design a global messaging system — 2B users, real-time delivery, offline queuing, per-conversation ordering, three-tick message status.
WebSockets Kafka Message Ordering Offline Delivery Backpressure Hot Partitions
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