Gmail Spam Filter
Design a real-time email ingestion and spam classification pipeline capable of evaluating incoming messages with ML heuristics, rule-based fallbacks, and user feedback telemetry.
URL Shortener
Build a high-performance URL shortening service like TinyURL or Bitly that generates 7-character aliases, handles 100:1 read-to-write ratios, and caches hot redirect lookups.
Distributed Rate Limiter
Design an edge-tier rate limiting system to protect APIs against abuse, credential stuffing, and DDoS using sliding-window counter algorithms and fast distributed caches.
Scalable Notification System
Architect a multi-channel notification engine supporting iOS APNS, Android FCM, SMS (Twilio), and transactional emails with priority routing and deduplication.
Distributed Cache Cluster
Design a distributed in-memory key-value caching system supporting consistent hashing, replication, write-through/write-back policies, and LRU eviction.
Cloud File Storage (Dropbox)
Design a cloud sync and file storage architecture featuring block-level chunking, deduplication, delta synchronization, and metadata version control.
YouTube Video Recommendation Engine
Design YouTube's two-stage recommendation pipeline: candidate generation (filtering millions to hundreds) followed by ranking & scoring for personalized user home feeds.
Netflix Home Page Recommendation
Design Netflix's personalized row generation system that curates customized titles, tailored artwork thumbnails, and dynamic row rankings for every member profile.
Real-Time Ride Matching & ETA Prediction
Architect Uber's dispatch and routing system combining geospatial H3 hex indexing, live GPS driver telemetry, graph routing engines, and surge pricing calculators.
Real-Time Payment Fraud Detection (Radar)
Design an ultra-low latency payment risk engine evaluating global network behavioral signals, velocity counters, and ML risk scoring before transaction authorization.
Typeahead Search Autocomplete
Design a high-availability typeahead suggestion service returning top 5 search completions within 20ms of every keystroke using distributed trie structures.
Amazon Item-to-Item Collaborative Filter
Design the 'Customers who bought this also bought' recommendation engine scaling to hundreds of millions of catalog products with precomputed item similarities.
Instagram News Feed & Photo Publishing
Design Instagram's timeline generation system supporting photo/video uploads, fanout-on-write for regular users, and fanout-on-read for celebrity accounts.
X (Twitter) Real-Time Trending Topics
Design a real-time stream processing pipeline to identify velocity spikes in hashtags and topics across regions with decay algorithms to prevent stale trends.
WhatsApp 1-on-1 & Group Chat
Design an end-to-end encrypted instant messaging platform supporting persistent connections, ephemeral delivery receipts, and efficient group message fan-out.
Distributed Web Crawler
Architect a scalable web crawler that downloads, parses, deduplicates, and indexes billions of web pages while strictly respecting robots.txt and politeness policies.
Search Engine Inverted Indexer
Design an inverted index and full-text search cluster supporting tokenization, TF-IDF / BM25 ranking, and distributed partition query execution.
Distributed Centralized Logging (ELK/Datadog)
Design a high-volume log aggregation pipeline that collects application stdout/syslogs across thousands of microservices, parses JSON structures, and supports real-time search.
Time-Series Metrics Monitoring (Prometheus)
Design a time-series telemetry monitoring system supporting pull/push metric collection, downsampling rollups, PromQL-style aggregation, and pager duty alerting.
Distributed Cron & Job Scheduler
Design a fault-tolerant distributed job orchestrator capable of triggering millions of delayed, recurring, and dependency-chained background tasks with at-least-once guarantees.