Practice
Real case studies that get harder as you go. Design systems, meet constraints, and see how they hold up in production.
Every challenge is built around production-style constraints: throughput, latency, storage scale, consistency tradeoffs, and failure handling.
A small bakery wants to launch a website for online orders. Design the backend for ~10 k daily visitors.
The bakery goes viral on social media. Handle 500 k daily visitors with caching and load balancing.
The bakery expands to 5 countries. Design for multi-region, currency, and localization.
Add real-time order tracking, kitchen displays, and survive an entire region going down.
Launch a ride-hailing app in a single city with real-time driver matching.
Expand to 20 cities, add surge pricing, and handle 1 M rides/day.
Operate in 50 countries with autonomous vehicles, ML-based dispatch, and five-nines uptime.
Build a simple social feed app with posts, follows, and a chronological timeline.
Handle 10 M users, celebrity fan-out, full-text search, and push notifications.
Scale to 500 M users, add video/image uploads, content moderation, and multi-region deployment.
Design a flash sale system where 1 M users compete for 10,000 items in 60 seconds.
Build a Slack-like team messaging app with channels, DMs, and presence indicators.
Add E2E encryption, cross-org messaging, and scale to 50 M users across regions.
Design a Netflix-like video streaming platform serving 100 M users worldwide.
Build a payment processing service for a mid-size e-commerce store handling 50 k transactions/day.
Scale to 50 M transactions/day across 30 countries with real-time fraud detection and multi-currency settlement.
Design a web crawler that indexes 10 M pages and serves keyword search results in < 200 ms.
Scale to 1 B pages with PageRank, autocomplete, personalized results, and multi-region serving.
Build a smart home platform connecting 100 k devices with real-time control and status updates.
Scale to 50 M industrial sensors with edge processing, anomaly detection, and five-nines uptime.
Design a Dropbox-like cloud storage service for 1 M users with sync, sharing, and versioning.
Scale to 100 M users with real-time co-editing, eDiscovery, data loss prevention, and multi-region replication.
Design a Ticketmaster-like platform handling 500 k users competing for seats in a 50 k-capacity venue.
Build a platform-wide notification service delivering 100 M messages/day across push, email, SMS, and in-app.
Design the architecture behind Twitter - tweets, timelines, trends, and search at 500 M+ users.
Design Instagram's photo/video sharing platform - feed generation, Stories, Reels, and Explore at 2 B users.
Design YouTube's video platform - upload, transcode, adaptive streaming, recommendations, and comments at planetary scale.
Design WhatsApp's messaging platform - E2E encryption, group chats, media, and offline delivery for 2 B users.
Design Uber's ride-hailing platform - real-time matching, surge pricing, ETA prediction, and global dispatch for 100 M+ users.
Design Spotify's music streaming platform - audio delivery, personalized playlists, offline mode, and social features for 600 M users.
Design Amazon's e-commerce platform - product catalog, cart, checkout, recommendations, and warehouse fulfillment at 300 M+ users.
Design Google Maps - map tile rendering, real-time navigation, traffic prediction, and place search for 1 B+ users.
Design Slack's team communication platform - channels, threads, search, file sharing, integrations, and enterprise compliance at 30 M+ DAU.
Design TikTok's short-video platform - video creation, For You feed, content moderation, and viral distribution for 1 B+ users.
Design Airbnb's marketplace - listing search, booking, payments, reviews, pricing, and trust at 150 M+ users.
Design Google Docs - real-time collaborative editing, conflict resolution, version history, and offline support for 1 B+ users.
Design Zoom's video conferencing platform - real-time video/audio, screen sharing, recording, and breakout rooms for 300 M+ daily participants.
Design a personal blogging platform where authors write posts and readers leave comments. ~5 k daily visitors.
Design a RESTful to-do list API with user accounts, lists, tasks, and due-date reminders.
Design a URL shortening service (like Bitly) that creates short links and tracks click analytics.
Design a Pastebin-like service for sharing text snippets with syntax highlighting and expiration.
Design a Linktree-like service where users create a personalized page with links to their social profiles.
Design a form submission backend that receives contact form data, validates it, and sends email notifications.
Design a simple polling/survey tool where users create polls, share them, and see real-time results.
Design a file upload and sharing service that handles uploads up to 100 MB with download links.
Design a weather API that aggregates data from multiple providers, caches results, and serves forecasts.
Design a browser-independent bookmark manager with folders, tags, search, and import/export.
Design a status page service (like Statuspage.io) showing uptime, incident updates, and health checks.
Design an email newsletter platform for creators to manage subscribers, write campaigns, and track opens.
Design a recipe sharing platform with ingredient search, meal planning, and grocery lists.
Design a QR code generation API that creates, stores, and tracks QR codes for URLs, text, and contact cards.
Design a real-time gaming leaderboard showing top players, rank lookups, and score history.
Design an image gallery service where users upload photos, organize them into albums, and share galleries.
Design a personal expense tracking app with categories, budgets, recurring expenses, and monthly reports.
Design an event creation and RSVP platform where organizers create events and guests respond.
Design a feature flag service that lets teams toggle features, run A/B tests, and do gradual rollouts.
Design a hosted changelog service where product teams publish release notes and users subscribe to updates.
Design a product search engine with faceted filters, autocomplete, spell correction, and relevance ranking for 5 M products.
Design an API gateway that handles routing, authentication, rate limiting, and request transformation for 50 microservices.
Design a distributed cron/job scheduler that runs millions of scheduled tasks reliably with retries and monitoring.
Design a content moderation system that screens text, images, and video using AI + human review for a social platform.
Design a CDN with edge caching, cache invalidation, origin shielding, and real-time purge support.
Design an OAuth2 identity provider with SSO, MFA, social login, session management, and RBAC for 1 M users.
Design a real-time analytics pipeline that ingests clickstream events and powers live dashboards with < 5 s latency.
Design a food delivery platform with restaurant listings, ordering, real-time driver tracking, and ETA estimates.
Design a centralized logging system (like Datadog Logs) that ingests, indexes, and searches 1 TB of logs per day.
Design a peer-to-peer video calling feature with signaling, NAT traversal, call history, and adaptive quality.
Design an appointment scheduling platform with availability management, booking, reminders, and waitlists for service businesses.
Design a real-time collaborative whiteboard (like Miro/Excalidraw) with drawing, shapes, sticky notes, and multi-user cursors.
Design an image optimization CDN that resizes, compresses, and converts images on-the-fly for web performance.
Design a managed DNS service with zone hosting, health-check routing, geo-based routing, and fast propagation.
Design an online code execution sandbox (like CodeSandbox / Replit) that runs user code safely with real-time collaboration.
Design a Hacker News / Reddit-style link aggregator with voting, ranking, comments, and anti-manipulation measures.
Design a CI/CD platform (like GitHub Actions) that runs build pipelines in isolated containers with parallel steps and artifact caching.
Design a multi-tenant SaaS backend with tenant isolation, per-tenant billing, custom domains, and data residency.