AI Architecture Coach Practice system design interviews with real-world challenges. Design the architecture, then generate it with AI to compare your approach.
8 challenges 15-35 min each Easy → Hard
Easy Web Services
Design a URL Shortener 15 min
Design a URL shortening service like bit.ly. It should generate short URLs, redirect to the original, and track click analytics.
Show hints (3) Think about the hash function for short codes How will you handle 301 vs 302 redirects? Where does click tracking data go? Show reference components (spoiler) API Gateway URL Service Redis Cache PostgreSQL Analytics Queue
Easy Real-time
Design a Chat Application 20 min
Design a real-time chat application like Slack. Support channels, direct messages, typing indicators, and message history.
Show hints (3) WebSockets for real-time, but what about offline users? How do you fan out messages to channel members? Consider message ordering and delivery guarantees Show reference components (spoiler) WebSocket Gateway Chat Service Presence Service Message Store Notification Service
Medium Location-based
Design a Ride-Sharing Service 25 min
Design the backend for Uber/Lyft. Match riders with nearby drivers in real-time, track locations, calculate fares, and handle payments.
Show hints (3) Geospatial indexing for nearby driver queries How do you handle the matching algorithm? Payment processing needs to be idempotent Show reference components (spoiler) API Gateway Matching Service Location Service (Redis Geo) Trip Service Payment Service Notification Service PostgreSQL Kafka
Medium Media
Design a Video Streaming Platform 30 min
Design Netflix's video streaming architecture. Support video upload, transcoding to multiple qualities, CDN delivery, and personalized recommendations.
Show hints (3) Video transcoding is CPU-intensive — how do you scale it? Adaptive bitrate streaming (HLS/DASH) Recommendation engine needs user watch history Show reference components (spoiler) CDN Transcoding Workers Object Storage (S3) Content Service Recommendation Engine User Service PostgreSQL Redis Kafka
Medium Social
Design a Social Media Feed 25 min
Design Twitter/X's news feed. Users post tweets, follow others, and see a personalized timeline. Handle celebrities with millions of followers.
Show hints (3) Fan-out on write vs fan-out on read — which and when? Celebrities need special handling (hybrid approach) Timeline caching is critical for read performance Show reference components (spoiler) API Gateway Tweet Service Timeline Service Fan-out Service Follow Graph (Neo4j) Redis Timeline Cache Kafka CDN
Hard Fintech
Design a Payment Processing System 30 min
Design Stripe's payment processing. Handle card authorization, capture, refunds, webhooks, PCI compliance, and multi-currency support.
Show hints (3) Idempotency keys are critical for payment safety PCI DSS requires network segmentation Eventual consistency — payment state machine Show reference components (spoiler) API Gateway (PCI Zone) Payment Orchestrator Card Vault (HSM) Ledger Service Webhook Service Fraud Detection PostgreSQL Kafka Redis
Hard Storage
Design a Distributed File Storage 35 min
Design Google Drive / Dropbox. Support file upload/download, sync across devices, sharing permissions, and real-time collaboration on documents.
Show hints (3) Chunked uploads for large files Conflict resolution for simultaneous edits How do you sync efficiently? (delta sync) Show reference components (spoiler) API Gateway Metadata Service Chunk Storage (S3) Sync Service Collaboration Service (OT/CRDT) Notification Service PostgreSQL Redis Kafka
Hard Infrastructure
Design a Search Engine 35 min
Design a web search engine. Crawl the web, build an inverted index, rank results by relevance, and serve queries with sub-100ms latency.
Show hints (3) Web crawler needs politeness policies and dedup Inverted index sharding strategy? PageRank for relevance, but what about freshness? Show reference components (spoiler) Web Crawler Cluster URL Frontier (Queue) Parser Service Inverted Index (Elasticsearch) Ranking Service Query Service CDN Object Storage Kafka