WhatsApp Architecture

Billions of messages a day with a famously small engineering team.

On the roadmap:Software Architect · step 5: Learn from the giants

Overview

WhatsApp relies on Erlang's lightweight processes to hold millions of persistent connections per server, with a store-and-forward model for message delivery.

Architecture highlights

Erlang/BEAM for massive concurrency
Persistent connections over a custom XMPP-derived protocol
Store-and-forward delivery with acknowledgements
End-to-end encryption using the Signal protocol

Architecture diagram

Key components

Chat servers
Hold long-lived client connections
Message queue / store
Holds messages for offline recipients
Presence service
Tracks online status and delivery receipts
Media storage + CDN
Stores and serves images, video and voice notes

Challenges and trade-offs

Connection density
Millions of sockets per host need cheap per-connection memory.
Offline delivery
Messages must be persisted until the recipient reconnects.
Encryption at scale
Key exchange and group fan-out must remain fast.

Study: WhatsApp

Learn how WhatsApp is built from the people who explain it. Watch first for the picture, then read for the detail.

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WHATSAPP System Design: Chat Messaging Systems for Interviews

Gaurav Sen · 2.1M views

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