System Design

Common System Designs

16 practice questions. Free questions open a full answer guide; the rest unlock with Pro.

  • Walk me through how you'd design a URL shortener like Bitly that handles a few thousand redirects per second. Mid level
  • Design a real-time recommendation system for an e-commerce platform serving 10 million daily active users.Go Pro Senior level
  • Design a retrieval-augmented generation (RAG) system that lets employees ask natural-language questions over an internal knowledge base of roughly 5 million documents.Go Pro Senior level
  • Design a feature-flag and progressive-delivery platform that internal product teams use to gate releases, run percentage rollouts, and target user segments. Walk through flag evaluation, how updates propagate, and how you keep it from becoming a single point of failure for every service that depends on it.Go Pro Staff-principal level
  • Your company's monolith needs to be decomposed into microservices. A migration will affect 50 engineers and take 2 years. How do you plan and execute this?Go Pro Staff-principal level
  • You're designing a multi-tenant SaaS platform on AWS where most tenants share infrastructure, but a few enterprise tenants demand a hard data-isolation guarantee and contractually capped blast radius. Design the tenant data-isolation architecture, including how you enforce isolation at runtime and how you'd onboard a tenant that needs to be fully siloed.Go Pro Senior level
  • Design a multi-tenant SaaS platform that isolates data between tenants while keeping operational complexity manageable. Discuss the isolation models and your recommendation.Go Pro Staff-principal level
  • Walk me through how you'd design the backend for a social media feed that shows each user a timeline of posts from the accounts they follow. How do you make the feed load fast?Go Pro Mid level
  • Design an end-to-end ML pipeline for detecting anomalies in time-series sensor data from 10,000 IoT devices.Go Pro Senior level
  • Design a zero-trust network architecture for a platform where engineers need to access production systems for debugging, but no persistent VPN or bastion host is acceptable.Go Pro Senior level
  • Design a deployment pipeline for a SaaS platform that must support both rapid feature iteration (multiple deploys per day) and enterprise customers who require change advisory board approval for every production change.Go Pro Senior level
  • Design a payment processing service that charges customers through a third-party gateway. A client may retry a request on a network timeout, and the same customer must never be double-charged.Go Pro Senior level
  • Design a globally distributed key-value store that targets single-digit millisecond reads anywhere in the world while supporting consistent writes.Go Pro Staff-principal level
  • Your team is building a shared internal developer platform (IDP). Design the self-service infrastructure provisioning layer — engineers should be able to provision a new microservice environment (VPC, ECS cluster, RDS, secrets, IAM roles) in under 10 minutes with guardrails enforced.Go Pro Senior level
  • Design the build and release pipeline for a container-based platform so that what runs in production is provably the exact code that came out of CI, with no way for a compromised build step or a malicious insider to slip in an unsigned or tampered image. How do you architect this supply-chain integrity end to end?Go Pro Senior level
  • Design a feature store for a company running 20 ML models across fraud detection, recommendations, and risk scoring.Go Pro Senior level
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