Design a Chat Application

Build a real-time messaging platform similar to Slack or Discord that supports direct messages, group chats, and channels.

Functional Requirements

• Real-time messaging with instant delivery
• Support for direct messages and group conversations
• Message history with search functionality
• File and media sharing within chats
• Online presence indicators and typing status
• Message reactions and threads

Non-Functional Requirements

• Sub-second message delivery globally
• Support millions of concurrent connections
• Message persistence and offline sync
• 99.9% availability

Questions to Consider

• What protocol will you use for real-time communication?
• How will you handle millions of concurrent WebSocket connections?
• How do you ensure message ordering and delivery guarantees?