System design interviews are the make-or-break round at top tech companies like Google, Meta, Amazon, Apple, and Netflix. Unlike coding questions, there's no single "correct" answer — interviewers are evaluating your ability to reason about trade-offs, scale, and architecture under pressure.
This article compiles the most popular and frequently-asked system design questions, each with a full expert-written solution you can study interactively on InterviewGPT.
Why System Design Interviews Are Different
Most candidates spend 90% of their prep on LeetCode and neglect system design. The truth? At senior and staff levels, system design often weighs more than coding in the final hiring decision.
Strong answers demonstrate:
- The ability to clarify requirements before diving in
- Back-of-the-envelope estimation (scale, storage, throughput)
- Knowledge of distributed systems fundamentals (consistency, availability, CAP theorem)
- Real-world technology choices (Kafka, Redis, PostgreSQL, etc.)
- An understanding of trade-offs — not just "what" but "why"
Top System Design Interview Questions & Solutions
🏦 Finance & Payments
High-Consistency Financial Ledger and Account Management System
Covers double-entry bookkeeping, ACID transactions, idempotency keys, and CQRS patterns.Scalable Payment Processing System
How to build a high-reliability payment gateway with retry logic and fraud detection hooks.Scalable Payment Gateway and Ledger Design
Deep-dive into dual-ledger architecture, reconciliation, and multi-currency handling.Scalable Digital Wallet System
Wallet balance management, atomic transfers, and eventual consistency patterns.Scalable Double-Entry Ledger System
How financial systems guarantee no money is ever created or destroyed.Low-Latency Stock Exchange Design
Order matching engines, LMAX disruptor patterns, and ultra-low latency storage.
💬 Messaging & Real-time Communication
Scalable Multi-Channel Notification System
Delivering 1 billion notifications/day via SMS, email, and push with priority queues.Real-Time Community Chat Platform
WebSocket-based real-time messaging, fan-out patterns, and message persistence.End-to-End Encrypted Messaging System
Signal protocol, key exchange, and forward secrecy in a messaging architecture.Instant Messaging System
How WhatsApp-style messaging handles offline delivery and message ordering.Scalable Real-Time Messaging System
Presence detection, read receipts, and message deduplication at scale.Team Collaboration & Messaging Platform
Slack-like systems: channels, threads, search, and real-time delivery.
📹 Video & Streaming
Video-on-Demand Streaming Service
Adaptive bitrate streaming, CDN design, and video encoding pipelines.Short-Form Video Platform
TikTok-style content delivery, recommendation hooks, and viral content propagation.Scalable Video Streaming Platform
Upload processing, transcoding pipelines, and global CDN distribution.Scalable Real-time Video Conferencing System
WebRTC, SFU vs MCU architectures, and packet loss compensation.Top-K Trending Videos System
Real-time leaderboards, approximate counting with Count-Min Sketch.
🌐 Social Networks & Feeds
Social News Feed
Fan-out on write vs read, ranking algorithms, and feed caching strategies.Social Media Microblogging Platform
Twitter-scale architecture: tweet storage, follower graphs, and timeline generation.Meta News Feed Design
The actual architecture powering billions of personalized feeds at Facebook.Professional Social Network
LinkedIn-style graph traversal, connection suggestions, and endorsements.Photo & Video Sharing Social Network
Instagram-scale media storage, CDN, and explore feed ranking.
🔗 Infrastructure & Storage
Distributed Key-Value Store
Building a DynamoDB/Redis-like system with consistent hashing and replication.Scalable Distributed Sharded KV Store
LSM-trees, Raft consensus, and petabyte-scale data distribution.Distributed In-Memory Cache
Memcached vs Redis, eviction policies, and cache stampede prevention.Distributed Rate Limiter
Token bucket, sliding window log, and distributed rate limiting with Redis.Distributed Message Queue
Kafka-style durable queues: partitioning, replication, and consumer groups.Object Storage System
S3-like systems: chunked uploads, erasure coding, and geo-replication.Cloud File Synchronization System
Dropbox-style delta sync, conflict resolution, and offline support.
🔍 Search & Discovery
Search Autocomplete System
Trie-based suggestions, personalization, and sub-100ms latency.Scalable Typeahead Suggestion System
Aggregation of trending queries and efficient prefix matching.Scalable E-commerce Search System
Elasticsearch at scale, faceted search, and relevance ranking.Google Maps System Design
Geospatial indexing, routing algorithms, and ETA computation.
🔗 URL & Crawling
Scalable URL Shortening System
Base62 encoding, redirect caching, and analytics tracking.Distributed Web Crawler Design
Politeness policies, frontier management, and deduplication at web scale.Scalable Web Crawler Design
BFS vs priority crawling, DNS caching, and robot.txt compliance.
🚗 Ride-Sharing & Location
Real-Time Ride-Sharing Architecture
Driver matching, geohash-based proximity, and surge pricing.Global Scalable Ride-Sharing System
Multi-region architecture for an Uber-scale platform.Scalable Nearby Friends System Design
Real-time location tracking, geofencing, and location privacy.
🏨 Booking & Reservations
Hotel Reservation System
Inventory management, double-booking prevention, and distributed locking.Scalable Movie Ticket Reservation System
Seat locking strategies, concurrency control, and payment flow.Online Travel Booking Platform
Flight search, dynamic pricing, and multi-vendor inventory aggregation.
🤖 AI & ML Infrastructure
Shared LLM Inference Platform
GPU batching, model serving, and multi-tenant LLM infrastructure.Domain-Specific LLM Fine-Tuning Platform
Dataset pipelines, training orchestration, and model versioning.Retrieval-Augmented Generation System
Vector databases, chunking strategies, and RAG evaluation frameworks.Agentic AI System
Tool-use, memory management, and reliability in multi-step AI agents.
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