Masst DocsHLD case studies
Here you'll have all the case studies
| Category | Example Systems | Core Modules / Key Patterns | Key Interview Points (Must Mention) |
|---|---|---|---|
| Coding / Learning Platform | - LeetCode - HackerRank - Udemy | - User Auth & Profiles - Content/Problem Management - Code Execution Sandbox - Submissions & Judging - Leaderboards - Discussion/Comments | - Secure user login & roles (student/instructor) - Code execution sandbox (isolation, scaling) - Problem CRUD & tagging - Leaderboards & ranking - Discussion forum & comments - Plagiarism detection |
| E-Commerce / Food Delivery | - Amazon - Flipkart - Swiggy - Uber Eats | - Product Catalog - Search & Filters - Cart & Checkout - Payment Gateway - Order Tracking - Logistics & Delivery - Recommendation Engine | - Product listing, search, filters - Cart & checkout - Payment gateway & fraud detection - Order tracking & notifications - Delivery partner app (for food) - Recommendation engine |
| Streaming Platforms | - Netflix - YouTube - Twitch | - Video Encoding & Storage - CDN Delivery - Live Streaming - Recommendation System - Comments/Chat - Subscription/Billing | - Video encoding & storage - CDN for content delivery - Recommendation engine (personalization) - Handling large-scale live streaming - Comments, chat, likes/dislikes - Monetization & subscription plans |
| Social Media | - Twitter - TikTok | - User Profiles - Posting/Feeds - Media Storage - Notifications - Search & Hashtags - Recommendation Feed | - Timeline/feed generation (ranking + caching) - Media storage & CDN - Hashtags/search - Notifications & messaging - Recommendation engine - Privacy settings & blocking |
| Online Multiplayer Games | - Chess.com - PUBG - Fortnite | - Real-Time Synchronization (WebSockets) - Matchmaking - Game State Management - Leaderboards - Chat | - WebSockets for real-time sync - Matchmaking logic (rank-based) - Game state consistency - Leaderboard management - Anti-cheat system - Replay or spectator mode (if relevant) |
| Collaborative Editing | - Google Docs - Figma | - Real-Time Document Sync (CRDT/OT) - Version Control - User Roles & Permissions - Conflict Resolution | - Real-time collaboration (CRDT or OT) - Document versioning & history - Access control (view/edit/comment) - Conflict resolution handling - Offline sync & merge |
| eSignature / Document Signing | - HelloSign - DocuSign - Adobe Sign | - User Authentication - Document Upload & Storage - Signature Workflow (sequential/parallel) - Audit Trail & Compliance - Notifications - API Integration | - Secure document upload & storage - Signature workflows (parallel, sequential) - Legal compliance & audit trail - Notifications/reminders - API integrations with apps (CRM, HR, etc.) |
| ATM / Banking System | - ATM networks - Core Banking | - Secure Authentication - Transaction Processing (ACID) - Cash Inventory - Audit Logging - Fraud Detection | - Card authentication (PIN, chip) - Transaction processing (withdraw, deposit, balance inquiry) - Cash inventory management - Audit logging & compliance - Network resilience & security |
| Stock Trading / Exchange | - NASDAQ - Coinbase | - Order Matching Engine - Market Data Streaming - Risk Checks - Transaction Settlement - High Availability | - Ultra-low latency order matching - Real-time market data streaming - Risk checks & fraud detection - Trade settlement workflows - Scalability (burst traffic) |
| Parking System | - Smart Parking - Mall Parking | - Slot Management - Ticketing - Payment System - Sensors (IoT) Integration - Availability Tracking | - Slot availability tracking - Ticket generation & validation - Payment integration - Pricing logic (per hour/duration) - IoT sensors for automation |
| Ride Sharing / Taxi App | - Uber - Lyft | - Driver-Rider Matching - Real-Time Location Tracking - ETA Calculation - Pricing Engine - Trip History | - Real-time location & route optimization - Driver-passenger matching - Dynamic pricing (surge pricing) - Trip history & ratings - Payment & fraud prevention |
| Messaging / Chat App | - WhatsApp - Slack - Telegram | - Real-Time Messaging (WebSockets) - Delivery Receipts - Media Upload - Push Notifications - Group Management | - WebSocket or long polling - Message delivery (1-1, group) - Read receipts & message states - Media (images, videos) storage - Push notifications |
| Email System | - Gmail - Outlook | - Email Sending/Receiving (SMTP/IMAP) - Queuing - Spam Filtering - Search & Indexing - Contact Management | - Mail delivery pipeline (queue-based) - Spam filtering (ML based) - Search & indexing - Contacts & address book - Attachment handling |
| Search Engine | - Google - Bing | - Web Crawling - Indexing - Ranking Algorithm - Autocomplete - Cache for Popular Queries | - Web crawler design - Inverted index for search - Ranking algorithm (PageRank, BM25) - Caching & autocomplete - Spam detection |
| Recommendation Engine | - Netflix Suggestions - Amazon “You may like” | - Collaborative Filtering - Content-Based Filtering - Ranking Algorithms - A/B Testing | - User-item rating matrix - Collaborative filtering - Ranking & personalization - A/B testing & feedback loops |
| IoT / Smart Systems | - Smart Parking - Smart Home | - Device Registration - Real-Time Data Ingestion - Stream Processing - Remote Control - Event Rules | - Device onboarding & authentication - Data streaming & processing - Remote command execution - Event-trigger rules engine |
| Payment Gateway | - Stripe - PayPal | - Secure Tokenization - Fraud Detection - Transaction Routing - Settlement - Refund Handling | - Payment flow (auth, capture, settle) - Fraud detection - PCI compliance - Retry mechanism & refunds - Multi-currency support |
| Subscription/Billing | - SaaS Billing Platforms | - Plan Management - Invoicing - Dunning (Retry Mechanism) - Tax Calculation - Usage Tracking | - Subscription lifecycle (new, renew, cancel) - Invoice generation - Dunning process for failed payments - Tax calculation & reporting |
| Analytics / Logging | - ELK - Splunk - Data Warehouses | - Log Collection & Aggregation - Search & Filtering - Metrics Dashboard - Alerts | - Centralized log ingestion - Indexing & search - Metrics visualization - Alerting & anomaly detection |
| URL Shortener | - Bit.ly - TinyURL | - Key Generation - Redirection - Click Analytics - Expiry Policies | - Unique short URL generation - Redirection handling - Click tracking analytics - Expiry & custom alias support |
| File Storage & Sharing | - Google Drive - Dropbox | - Chunked Upload - File Sync - Sharing & Permissions - Versioning - Metadata Search | - File chunking & upload - Syncing across devices - Sharing permissions (read/write) - Version history & restore |
| API Gateway / Rate Limiter | - Kong - Nginx | - API Gateway Reverse Proxy - Token Bucket/Leaky Bucket Rate Limiting - Authentication - Request Routing | - API request routing - Authentication & authorization - Rate limiting (token bucket/leaky bucket) - Monitoring & analytics |
System Design Guide
A comprehensive guide for learning and mastering system design concepts, HLD and LLD case studies.
HelloSign (Dropbox Sign)
📝 HelloSign serves millions of users globally, processing millions of legally binding e-signatures monthly. This document outlines the comprehensive architecture that enables secure, compliant, and seamless digital signature workflows with 99.99% availability.