High-Level Design Problems
Distributed architectures with diagrams, technology choices, deep dives, and trade-offs. Built for interviews at Amazon, Google, Meta, and top startups.
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Start with HLD Fundamentals — covers CAP theorem, caching, sharding, queues, and back-of-envelope estimation.
Step-by-step delivery structure for your system design interview. Timings, phases, and what to say at each stage.
One-page reference: when to use Kafka, Redis, databases, caching strategies, sharding, real-time patterns, capacity estimation formulas, and trade-off one-liners.
Beginner
6 problemsReal-Time Leaderboard
Redis sorted sets, top-N queries, real-time ranking at scale.
Rate Limiter
Token bucket, sliding window, distributed limiting with Redis Lua scripts.
Pastebin / Text Sharing
Unique ID generation, object storage, CDN caching, and expiry cleanup. The easiest full system design.
Unique ID Generator
Snowflake IDs, UUID, range allocation, clock skew. The building block every distributed system needs.
Key-Value Store (Redis / DynamoDB)
Consistent hashing, replication, quorum reads/writes, LSM trees. Foundation of all distributed DBs.
URL Shortener (Bitly / TinyURL)
Base62 encoding, Snowflake IDs, CDN caching, click analytics pipeline.
Intermediate
12 problemsTwitter (X) / Threads — Social Feed
Fan-out on write vs read, timeline caching, celebrity problem.
Chat System (WhatsApp / iMessage)
WebSocket connections, offline delivery queues, Cassandra message store.
Notification System
Multi-channel push/email/SMS, Kafka pipelines, template service, engagement tracking.
Photo Sharing (Instagram / Pinterest)
Media upload pipeline, CDN delivery, news feed generation, fan-out, image optimization.
Ticket Booking (BookMyShow / Ticketmaster)
Seat selection, distributed locking, temporary holds, payment integration, no double-booking.
News Aggregator (Google News)
Crawling 50K sources, story clustering with embeddings, personalized feed ranking, breaking news detection.
Search Autocomplete / Typeahead
Trie data structure, prefix matching, real-time trending detection, caching hot prefixes.
Nearby Service (Yelp / Google Maps)
Geohash, quadtree, spatial indexing, high-frequency location updates, radius queries.
Shopping Cart (Amazon / Flipkart)
Cart persistence across devices, guest-cart merge on login, flash-sale write bursts.
Q&A Forum (Quora / StackOverflow)
100:1 read skew, answer ranking, full-text search over 10M questions.
Image Processing Microservice
Async pipeline with presigned URLs, worker pools, libvips streaming, idempotency cache, auto-scaling on queue depth.
Business Rules Engine
Expression parsing to AST, Rete algorithm for 10K rules in 50ms, hot reload via Kafka, action execution with DLQ.
Distributed Cache
Consistent hashing with virtual nodes, approximated LRU eviction, hot key replication, and stampede control.
Spotify / Music Streaming
Pre-transcoded bitrate ladders, CDN chunk delivery, gapless prefetch, offline DRM, and royalty-grade play counting.
Advanced
17 problemsDistributed Job Scheduler
Redis ZSET hot window, leader election, retries, dead-letter queues.
Delayed Trigger Service
SQS + Cassandra, hierarchical timing wheels, circuit breaker patterns.
Digital Wallet (PhonePe / Venmo)
Double-entry ledger, idempotency keys, reconciliation, saga pattern.
Food Delivery (Zomato / Uber Eats)
Elasticsearch search, Redis Geo proximity, dispatch algorithms, live tracking via WebSockets.
Stock Broker (Robinhood / Zerodha)
Order matching engine, CQRS event sourcing, exactly-once delivery, Kafka, real-time notifications.
Ride Sharing (Uber / Lyft)
Real-time driver matching, location tracking, ride lifecycle, surge pricing, ETA calculation.
Video Streaming (Netflix / YouTube)
Video encoding pipeline, CDN edge caching, adaptive bitrate streaming, recommendation engine.
Collaborative Editing (Google Docs / Notion)
Real-time multi-user editing, OT/CRDT conflict resolution, presence tracking, version history.
Cloud File Storage (Dropbox / Google Drive)
Chunking, content-addressed dedup, delta sync, conflict resolution, version history.
Metrics Monitoring (Datadog / Prometheus)
Time-series ingestion, Gorilla encoding, rollup aggregation, real-time alerting pipeline.
Ad Serving and Auction System
Real-time bidding, ML ad ranking, budget pacing, click fraud detection, impression tracking.
Payment System (Stripe / Razorpay)
Payment orchestration, idempotency, double-entry ledger, settlement, reconciliation, PCI compliance.
Distributed Message Queue (Kafka)
Partitioned commit log, consumer groups, exactly-once delivery, ISR replication, ordering guarantees.
Web Crawler & Search Engine
Two-level URL frontier for politeness, Bloom-filter dedup, sharded inverted index.
ChatGPT / Claude (AI Chat)
Token streaming over SSE, GPU inference scaling, context-window management, per-tier rate limits.
Freight Logistics System
Truck allocation, real-time tracking, route optimization, and ETA computation at scale.
Real-Time Load Bidding
Auction marketplace for freight loads, sorted sets for ranking, WebSocket fan-out for live updates.
E-Commerce Platform
Preventing oversell with conditional updates and reservations, order sagas on a durable workflow, checkout idempotency, CDC-fed search.
Trending Topics / Top K
Count-Min Sketch, Space-Saving heavy hitters, two-tier top-K aggregation, sliding windows, and rate-of-change ranking.
Recommended Study Order
Follow this progression to build concepts layer by layer. Each level builds on the previous.