Practice series
Caching, partitioning & hot-path scale
Hot keys, cache strategy, sharding, admission control, quotas, and durable fast paths.
- 01Free
Ad Click Aggregator
Design an ad click aggregation system that ingests millions of click events per second and serves near-real-time plus historical aggregate metrics to advertiser...
Meta - 02Preview
AI Agent System
Design a production AI agent application platform that accepts user goals, manages context and memory, calls tools safely, pauses for human review when needed,...
Practice bank - 03Preview
Chat Service
Design the backend infrastructure behind a chat product — stateful connection servers, message storage, and group fan-out — for hundreds of millions of concurre...
Discord - 04Preview
Coupons and Deals Platform
Design a coupons and deals platform where users browse and search a large, frequently changing catalog of deals and redeem coupon codes exactly once per limit,...
Practice bank - 05Preview
Donation Platform
Design a donation platform like GoFundMe — a campaign can go viral overnight and receive a massive spike of small donations, and every dollar must be captured,...
Practice bank - 06Preview
Facebook Post Search
Design search over a social feed — let users find posts by keyword in near real time while respecting each post’s privacy/visibility settings.
Meta - 07Preview
Flash Sale
Design a flash sale system where a limited quantity of a hot item goes on sale at a fixed instant and receives a 1000x traffic spike in seconds — inventory must...
Practice bank - 08Preview
Game Leaderboard
Design a real-time game leaderboard that ranks millions of players by score, supports regional and time-windowed boards, and serves both top-N and a given playe...
Strava - 09Preview
Hotel Reservation (Booking.com)
Design Booking.com — a hotel marketplace aggregating live availability and pricing from thousands of independent supplier hotels, where search results must stay...
Booking.com - 10Preview
Metric Monitoring and Alerting
Design the metrics pipeline behind a monitoring platform — the path from an SDK on thousands of hosts emitting numeric measurements, through streaming pre-aggre...
Uber - 11Preview
Ticketmaster (General Admission)
Design Ticketmaster for general-admission events — there is no seat map, only a fixed capacity count per ticket tier, and the system must sell tickets correctly...
Ticketmaster - 12Free
Ticketmaster
Design Ticketmaster — an event ticketing system that sells reserved seats under extreme flash-sale contention without ever double-selling a seat.
Ticketmaster - 13Free
Top K Songs (Spotify)
Design Spotify's Top-K most-played songs feature — compute top charts over sliding time windows at listening-event scale.
Spotify / Meta - 14Free
Uber (Ride Hailing)
Design Uber — a ride-hailing platform matching riders to nearby drivers in real time, with live location tracking, pricing, and trip lifecycle management.
Uber - 15Free
Web Crawler
Design a web-scale crawler that politely fetches and indexes billions of pages, deduplicates content, and keeps the corpus fresh.
Google - 16Preview
Yelp
Design Yelp — a local business search and review platform that returns nearby, filterable business results ranked by relevance and rating.
Yelp - 17Free
- 18Free
LLM Inference Gateway
Design an LLM inference gateway that sits between internal product teams and multiple model providers/backends, handling routing, streaming, quotas, and safety...
OpenAI / Anthropic - 19Preview
AI Training Cluster
Design the scheduler for a large GPU/TPU training cluster shared by multiple teams running distributed training jobs, handling gang scheduling, preemption, and...
Meta - 20Preview
- 21Preview
Vector Database
Design the storage and query engine of a vector database that indexes billions of embeddings for approximate nearest-neighbor search.
Meta (Faiss) - 22Preview
Distributed Key-Value Store
Design a Dynamo-style highly available key-value store: partition keys across nodes with consistent hashing, replicate each key to N nodes, and let every operat...
Practice bank - 23Preview
Distributed Cache
Design a distributed in-memory cache service at Redis/Memcached scale that serves roughly 1M QPS at p99 under 5ms.
Meta - 24Preview
Distributed Message Queue
Design a Kafka-style durable, partitioned log broker that ingests high-throughput event streams.
Apache Kafka (LinkedIn) - 25Preview
Food Delivery Marketplace
Design a DoorDash-style food delivery marketplace connecting consumers, Dashers, and merchants.
Uber - 26Preview
Live Comments
Design a live comments system that fans out comments from one live event to millions of concurrent viewers in real time.
Meta