System Design: Real-Time Bidding (RTB) Platform — Ad Auction in 100ms (2025)
RTB Architecture Overview Real-Time Bidding is the programmatic ad auction system that runs every time a user loads a web […]
System Design
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System Design
Learn to design scalable, reliable systems that handle millions of users. System design interviews test your ability to architect real-world applications, considering tradeoffs, scalability, and best practices.
Core Topics:
Scalability: Load balancing, horizontal vs vertical scaling
Storage: Databases (SQL vs NoSQL), caching (Redis, Memcached)
Reliability: Replication, failover, disaster recovery
Performance: CDNs, caching strategies, database indexing
Common Design Questions:
Design URL shortener (bit.ly)
Design rate limiter
Design Twitter/Instagram feed
Design messaging system (WhatsApp)
Design file storage (Dropbox)
Interview Level: Senior engineers (L5+) at FAANG companies. Requires 3-5+ years experience to tackle effectively.
Preparation: Study system design patterns, understand distributed systems fundamentals, and practice mock interviews.
System Design
System Design: Access Control and Authorization — RBAC, ABAC, and Policy Enforcement (2025)
Authorization Models ACL (Access Control List): per-resource list of who can do what. Simple but does not scale — updating
System Design
Low-Level Design: Issue Tracker — Workflow State Machine, Search, and Notifications
Core Entities Issue: issue_id, project_id, title, description (rich text), type (BUG, FEATURE, TASK, EPIC), status, priority (P0-P3), assignee_id, reporter_id, parent_issue_id
System Design
System Design: ML Training and Serving Pipeline — Feature Store, Training, and Inference at Scale (2025)
ML Platform Architecture Overview An ML platform has three distinct phases: Feature Engineering — transform raw data into model-ready features
System Design
Low-Level Design: Stock Trading Platform — Order Matching, Portfolio, and Risk Checks
Core Entities Account: account_id, user_id, account_type (CASH, MARGIN), buying_power, portfolio_value, status. Order: order_id, account_id, symbol, side (BUY/SELL), type (MARKET, LIMIT,
System Design
System Design: A/B Testing Platform — Experiment Assignment, Metric Collection, and Statistical Analysis
Requirements An A/B testing platform enables product teams to run controlled experiments: show variant A to 50% of users and
System Design
Low-Level Design: Event Management System — Venue Booking, Ticketing, and Attendee Management
Core Entities Venue: venue_id, name, address, capacity, type (ARENA, CONFERENCE_CENTER, THEATER, OUTDOOR), facilities (JSON: {parking, catering, av_equipment}), timezone, is_active. Event:
System Design
Low-Level Design: Subscription Service — Plan Management, Billing, Dunning, and Entitlements
Core Entities Product: product_id, name, description, type (SAAS, MEDIA, PHYSICAL). Plan: plan_id, product_id, name, billing_period (MONTHLY, QUARTERLY, ANNUAL), price, currency,
System Design
System Design: Vector Database — Embeddings Storage, ANN Search, and Semantic Retrieval
What is a Vector Database? A vector database stores high-dimensional numerical vectors (embeddings) and supports efficient similarity search: “find the
System Design
Low-Level Design: Banking System — Accounts, Transactions, Transfers, and Fraud Monitoring
Core Entities Customer: customer_id, first_name, last_name, email, phone, date_of_birth, ssn_hash, kyc_status (PENDING, VERIFIED, REJECTED), address, created_at. Account: account_id, customer_id, account_number
System Design
Low-Level Design: Appointment Scheduling System — Availability, Booking, and Calendar Sync
Core Entities Provider: provider_id, user_id, name, type (DOCTOR, CONSULTANT, TRAINER, THERAPIST), timezone, bio, photo_url, is_active. Service: service_id, provider_id, name, duration_minutes,
System Design
System Design: Drone Delivery Platform — Fleet Management, Route Planning, and Airspace Coordination
Requirements A drone delivery platform dispatches autonomous drones to deliver packages from warehouses or stores to customer addresses. Core challenges:
System Design
Low-Level Design: Library Management System — Catalog, Borrowing, Reservations, and Fines
Core Entities Book: book_id, isbn, title, authors (array), publisher, published_year, genre, language, description, cover_url. BookCopy: copy_id, book_id, library_id, condition (NEW,
System Design
System Design: IoT Data Platform — Device Ingestion, Time-Series Storage, and Real-Time Alerting
Requirements An IoT data platform ingests telemetry from millions of connected devices — sensors, smart meters, industrial equipment, wearables —
System Design
Low-Level Design: Parking Lot System — Space Management, Ticketing, and Dynamic Pricing
Core Entities ParkingLot: lot_id, name, address, total_floors, total_spaces, open_time, close_time, timezone. ParkingFloor: floor_id, lot_id, floor_number, total_spaces, available_spaces. ParkingSpace: space_id, floor_id,