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Atlassian mock interview System Design Prompt 3

javasleep

March 19, 2025

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🧩 System Design Prompt #3: Design a Collaborative Document Editing Platform (like Confluence)

🎯 Prompt:

Design a simplified version of Confluence where multiple users can:

• Create and edit documents (rich text)
• Collaborate in real time (see each other’s edits)
• Comment on sections of the document
• Version history and rollback
• Access control (read-only, edit, admin)

The system should support teams with thousands of users and large documents.

✅ What You’re Being Tested On:

• Real-time collaboration and concurrency
• Rich document storage and versioning
• Access control and permission systems
• Scalability under team-based usage
• Syncing updates across clients

🧠 What You Should Cover:

1. Clarify the Requirements

Ask things like:

• Do we need Google Docs–level real-time editing?
• How big can documents be?
• Should edits be autosaved? If so, how frequently?
• What types of roles or permissions are needed?

2. Core Features

• Create/edit documents (markdown or rich-text)
• Real-time updates via WebSocket or polling
• Comments on text blocks
• Version control (auto-save history)
• Permissions: owner, editor, commenter, viewer

3. System Components

📎 Frontend Client

• Rich text editor with WebSocket client
• Autosave logic and sync with server

⚙️ Backend Services

• Document Service: create, update, store documents
• Collaboration Service: manages live editing sessions (WebSockets)
• Comment Service: attach comments to paragraphs or ranges
• Versioning Service: saves historical snapshots
• Permission Service: handles access roles

4. Data Model

documents

document_id UUID PRIMARY KEY
title TEXT
owner_id UUID
content JSONB (structured blocks)
created_at, updated_at

document_versions

version_id UUID
document_id UUID
content JSONB
created_at
created_by

comments

comment_id UUID
document_id UUID
text TEXT
range_start, range_end (or block reference)
created_by, created_at

permissions

document_id UUID
user_id UUID
role ENUM('owner', 'editor', 'commenter', 'viewer')

5. Real-Time Collaboration (CRDT / OT)

To handle multiple users editing the same doc at once:

• Use CRDT (Conflict-Free Replicated Data Types) or Operational Transformation (OT).
• CRDTs are more modern and peer-friendly.
• Use WebSockets to:
  • Broadcast operations (insert/delete/change) to other collaborators
  • Maintain in-memory “editing sessions” per document
• Sync changes every few seconds to a durable store.

6. Versioning and Rollbacks

• Save a version every X minutes or on significant changes.
• Store diffs or snapshots (tradeoff: space vs speed).
• Allow users to view and restore previous versions.

7. Access Control

• Enforced at the API and database level.
• Use middleware or permission service to check role on each request.
• Owners can share or revoke access.

8. Scalability Considerations

• Session Store: Use Redis or in-memory cache for tracking who’s collaborating on what
• WebSocket Scaling: Use a pub/sub layer (e.g., Redis Streams or Kafka) for syncing across nodes
• CDN for static assets
• Document partitioning/sharding if the data set becomes large
• Limit document edit concurrency if needed

9. Advanced Features (Nice to Have)

• Inline commenting (like Google Docs)
• Offline editing + sync
• Email/webhook notifications for doc activity
• Document templates
• Analytics: page views, top editors