WhatsApp Messaging System

WhatsApp / Meta

WhatsApp delivers billions of messages daily to 2B+ users with end-to-end encryption and sub-second delivery. The architecture centers on persistent WebSocket connections managed by a connection service, with an intelligent message router that handles online delivery instantly and queues messages for offline recipients. Designed for teams building encrypted messaging platforms that prioritize delivery reliability and end-to-end privacy at scale.

Data Flow

WebSocket API

Connection Manager

Message Router

Presence Service

Offline Queue

Active Sessions

Messages Store

Media Storage

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Service Breakdown (8 services)

Compute3 services

Connection Manager

•Runs containerized microservices at scale
•Auto-scales based on CPU and memory utilization
•Supports rolling deployments and health checks

Message Router

•Runs containerized microservices at scale
•Auto-scales based on CPU and memory utilization
•Supports rolling deployments and health checks

Presence Service

•Runs containerized microservices at scale
•Auto-scales based on CPU and memory utilization
•Supports rolling deployments and health checks

Storage1 service

Media Storage

•Stores objects with eleven 9s of durability
•Supports lifecycle policies for cost optimization
•Serves as a data lake foundation

Networking1 service

WebSocket API

•Routes and throttles incoming API requests
•Enforces authentication and rate limiting
•Provides a unified entry point for microservices

Messaging1 service

Offline Queue

•Decouples services with reliable message queuing
•Supports standard and FIFO delivery modes
•Scales automatically with message volume

Data2 services

Active Sessions

•Caches hot data in-memory for sub-ms latency
•Supports Redis and Memcached engines
•Reduces database load with intelligent caching

Messages Store

•Provides single-digit millisecond reads and writes
•Scales throughput automatically with demand
•Supports global tables for multi-region access

Scaling Strategy

Connection managers scale horizontally with each instance handling thousands of WebSocket connections. The message router uses ElastiCache to look up which connection manager holds each recipient's session. Offline messages queue in SQS with per-user ordering, and DynamoDB stores message history with TTL-based expiry. Media uploads go directly to S3 with pre-signed URLs to avoid bottlenecking the message path.