Coders Crushby Napplied AI
HARD

Design WhatsApp Messaging System

Design a real-time messaging application like WhatsApp supporting 1-on-1 chat, group chat, media sharing, and message delivery receipts.

Estimated Time: 45 minutes
#messaging#websockets#real-time#distributed

Solution Overview

WhatsApp architecture: WebSocket connections for real-time messaging, message queue for offline delivery, distributed database for message persistence, CDN for media files, push notification service, end-to-end encryption.

Solution Overview

WhatsApp architecture: WebSocket connections for real-time messaging, message queue for offline delivery, distributed database for message persistence, CDN for media files, push notification service, end-to-end encryption.

Hints to Get Started
1

Start with 1-on-1 messaging

2

Consider offline message delivery

3

How to handle read receipts?

Scalability Strategies
  • •Shard by user_id
  • •Message retention policy (30 days)
  • •CDN for media
  • •Redis for online presence
Components
  • •WebSocket Gateway
  • •Message Queue (Kafka)
  • •User Session Manager
  • •Message Store (Cassandra)
  • •Media Storage (S3)
  • •Push Notification Service
Message Flow
  • •Client → WebSocket → Message Queue → Recipient WebSocket → ACK
  • •If offline: Store in queue → Push notification → Deliver on reconnect
Database Design

messages

message_id, sender_id, recipient_id, content, timestamp, status

conversations

conversation_id, participants[], last_message, last_read

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