📝 System Design: Google Docs with Real-Time Collaboration (Frontend Interview Guide)
Category: system-design
Difficulty: hard
Target Level: Senior Frontend Engineer / Staff Engineer Duration: 45-60 minutes Interview Focus: Real-time Collaboration, Conflict Resolution, State Synchronization, Performance Interview Approach & What Interviewers Look For When asked to design Google Docs in a frontend interview, interviewers are evaluating: Real-time Collaboration: Can you design a system where multiple users can edit simultaneously without conflicts? Conflict Resolution: Do you understand Operational Transformation (OT) or CRDTs? State Management: How do you keep local and remote state synchronized? Performance: Can you handle large documents (100k+ characters) without lag? Offline Support: How do you queue changes when the user is offline? Scalability: Can your design support 50+ concurrent editors? Pro Tip: Start by clarifying the scope, then dive into the collaborative editing algorithm (OT/CRDT), followed by architecture and implementation details. Clarifying Questions (First 5 minutes) Before diving in, ask these questions to scope the problem: Functional Scope: "Should we support just text editing, or also rich formatting (bold, italics, images)?" "Do we need real-time cursor positions and presence indicators?" "Should we support comments and suggestions mode?" "Do we need version history and document recovery?" Non-Functional Requirements: "How many concurrent users per document? 5? 50? 500?" "What's the target latency for edits to appear on other clients? <100ms?" "Should we support offline editing with sync when reconnected?" "What about conflict resolution when two users edit the same character?" Technical Constraints: "Can we use WebSockets, or should we support HTTP-only environments?" "Browser support? Modern browsers only?" "Should we persist every keystroke, or batch updates?" High-Level Architecture (Draw This!) ``` ++ UI Layer (React/ContentEditable) • Editor Canvas • Toolbar • Comments Panel Local State (CRDT/OT Document Model) • Text Content • Formatting • Cursor Positions Sy...