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