Problem Statement

Design a messenger platform that can serve for around more than 100M users. The platform supports web and mobile apps(android, ios).

Gathering Requirements

• Chatting:
  • Support one-on-one conversation.
  • Support group chat that has more than 1000 users per group.
  • Support those who already read the last message.
  • Support message sent time and message read time per user.
• Sending file, and attachment in a conversation:
  • Maximum size of a file, attachment is 5MB.
  • Maximum per sending is 5 files.
  • Just support image types(jpg, jpeg, png, SVG, ...) or document types(doc, docx, csv, xlsx).
  • Support emoji reaction for each message.
• Story video:
  • User can post brief videos.
  • User can post 10 brief videos per day.
  • Video duration must not exceed 60 seconds.
  • Support emoji reaction for each video.

Capacity Planning

• Number of users on the application every month: 1M
• Number of active users per second at peak traffic: 500K
• Number of messages per second at peak traffic: 10M
• Estimate Database store size: 1M users * 5KB per user

High-level Design

General Design

Chatting Design

Emoji Design

Protocols

Database

• Pros/Cons Between databases
• Decided or Plan

API Design

Monitoring

1. Availability SLA: p99.999
2. Latency SLA: p99.99 of 5 milliseconds