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WhatsApp System Design
Visual Problem Diagram
Scenario
Imagine billions of people treating chat like a utility—one tap to send, one glance at delivery ticks, and trust that no one at the company can read the thread. Within seconds of a viral moment, a family group shares a video, a stadium channel floods with reactions, and millions of phones retry the same send on bad train Wi‑Fi. Designing messaging that stays private, ordered, and instant under that pressure is a classic large-scale system design challenge.
Design a messaging platform like WhatsApp with one-on-one and group chat, delivery and read receipts, and end-to-end encryption. Real production systems separate small control messages (text, receipts, presence) from large media files (photos, video). Mobile networks retry—your design must handle duplicate sends and still show messages in the right order.
You should support encrypted messaging, offline catch-up, groups, presence, and media attachments. Be ready to explain per-chat sequence numbers, the inbox model, and group fan-out limits without diving into full cryptographic proofs unless the interviewer asks.
Constraints
1:1 and group chat, text/media, receipts, E2E encryption, offline delivery, presence
< 100 ms signaling target online, 99.99% availability, ordered per-chat delivery
2B users, 1B DAU, ~50B messages/day (~600K/s peak), ~10 TB/day storage growth
Stages ahead
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