Design Whatsapp

• 1. Clarify the requirements
• 2. Capacity estimation
• 3. User discovery
• 4. Sending a 1:1 message
• 5. Receiving a 1:1 message
• 6. Delivery and read receipts
• 7. Presence: online, last seen, and typing
• 8. Sending media
• 9. Group messaging
• 10. Large groups and broadcast
• 11. Push notifications