System design guide
System design interview guides
Each guide walks one question the way a strong candidate would in a 45-minute round: requirements, estimates, a diagram, the data model, how it scales, and the follow-ups interviewers like to ask. Preparing for coding rounds too? Interview LLM covers those.
Method
A system design interview framework you can run in 45 minutes
Requirements, estimates, API, high-level design, deep dive, trade-offs: a time-boxed template with what interviewers grade at each step.
Back-of-the-envelope estimation for system design interviews
The numbers worth memorising, a 5-step method, and worked QPS, storage and bandwidth estimates you can reuse in any design round.
Core concepts
Caching strategies for system design interviews
Cache-aside, read-through, write-through, write-back and write-around; eviction, invalidation, stampedes and hot keys, and when to use each in an interview.
Sharding and consistent hashing for system design interviews
Range, hash and directory sharding, choosing a shard key, consistent hashing with virtual nodes, hot partitions, cross-shard queries and resharding.
Consistency models, CAP and PACELC for system design interviews
Strong, eventual, causal and read-your-writes consistency; quorums; what CAP and PACELC actually say, and how to choose for each part of a design.
Classic design questions
Design a URL shortener (TinyURL / Bitly)
Requirements, QPS and storage estimates, ID generation (base62 vs hashing vs counters), schema, caching, and the follow-ups interviewers ask.
Design a distributed rate limiter
Token bucket vs sliding window, Redis-backed counters, multi-region limits, headers and failure modes, with a diagram and common follow-ups.
Design a social news feed
Fan-out on write vs read, the celebrity problem, feed ranking, cache layout and pagination, with estimates, a diagram and common follow-ups.
Design a chat app (1:1 and group messaging)
WebSockets, message ordering, delivery receipts, presence, storage and group fan-out, with estimates, an architecture diagram and follow-ups.
Design a notification system (push, email, SMS)
Queues, retries, deduplication, user preferences, rate caps and provider failover, with a diagram, data model and common follow-ups.
Design a web crawler
URL frontier, politeness, robots.txt, deduplication with Bloom filters, and scaling fetchers to billions of pages, with estimates, a diagram and follow-ups.
Design a distributed cache
Partitioning with consistent hashing, replication, eviction, hot keys, cache stampedes and failure handling, with estimates, a diagram and follow-ups.
Design a ride-sharing app (Uber / Lyft)
Driver location ingestion, geospatial indexing, matching and dispatch, trip state, ETA and surge pricing, with estimates, a diagram and follow-ups.
Design a payment system
Idempotency keys, payment state machines, double-entry ledgers, PSP integration, webhooks and reconciliation, with estimates, a diagram and follow-ups.
Design a video streaming platform (YouTube / Netflix)
Resumable uploads, a transcoding pipeline, adaptive bitrate streaming (HLS/DASH), CDN delivery and metadata, with estimates, a diagram and follow-ups.
Design a top-K system and real-time leaderboard
Heavy hitters, trending items and game leaderboards: count-min sketch, sliding windows, Redis sorted sets, and the batch-plus-stream pattern, with a diagram.
Company rounds
Meta product architecture vs system design: what's different
How Meta's two design rounds differ (product APIs and data models vs infrastructure at scale), how candidates end up in each, and how to prepare.
The Google system design interview: format, focus and prep
How Google's system design round works by level, what interviewers look for, typical prompts, and a prep plan, based on public candidate reports.
The Amazon system design interview: format, Leadership Principles and prep
Where system design sits in Amazon's SDE loop, how Leadership Principles show up in the design round, typical prompts, and how to prepare.
The Uber system design interview: real-time, geospatial and prep
What Uber's system design round tends to focus on (real-time location, dispatch, ETAs, payments), reported prompts, and how to prepare.
The Stripe system design interview: reliability, APIs and prep
How Stripe's design and API rounds reportedly work, why idempotency and failure handling dominate, typical prompts, and a focused prep plan.