Chat System Design (WhatsApp / Messenger Architecture) | System Design Tutorial

In this video, I’ll walk you through the complete Chat System Design, covering both functional and non-functional requirements of a real-time messaging platform — just like WhatsApp, Slack, or Messenger.

We’ll start with the high-level architecture, then dive deep into how 1:1 and group chat, online/offline status, message history, and read receipts actually work behind the scenes.

Finally, we’ll cover key non-functional requirements like low latency, scalability, reliability, and fault tolerance — and see how they influence our design choices.

🔹 Topics Covered:

Functional requirements overview

1:1 and group chat flow

Online/offline status and presence servers

Message history retrieval

Read receipts (sent → delivered → read)

Non-functional requirements deep dive
(low latency, scalability, reliability, fault tolerance)

This video is perfect for system design interviews, backend engineers, or anyone curious about how chat applications are built.
0:00 - Introduction and Requirements Overview
1:48 - High-Level Architecture
5:00 - 1:1 Chat Flow
9:00 - Multi Device Synchronization
10:38- Group Chat Flow
12:45-Online/Offline Status
16:34-Message History and Read Receipts Flow
20:00-Non-Functional Requirements
23:40-Wrap Up
#SystemDesign #ChatAppArchitecture #backendengineering #SoftwareDesign #techtutorial

Видео Chat System Design (WhatsApp / Messenger Architecture) | System Design Tutorial канала Design Decode Camp