Interview study guide
System design, reasoned out.
Both rounds: the classic backend design interview and the frontend system design interview. Every building block comes with a small model you can run, every estimate is calculated, and every case study follows the same shape from requirements to trade-offs.
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01The System Design InterviewWhat the round measures, a framework you can run every time, requirements that drive the design, estimates calculated in code, the latency and availability numbers to defend them, and how to draw and talk through it all.02Scaling FundamentalsGetting from one server to many: scaling up vs out, stateless services, load balancers and their algorithms, failover, DNS and CDNs, gateways, autoscaling and running in several regions.03CachingWhere copies of answers live, from the browser to the database: how they're filled, evicted and invalidated, and how a cache cluster survives hot keys, stampedes and lost nodes, decided at the design level with runnable models.04Data StorageChoosing and shaping the data layer at the design level: access patterns, replication, sharding and hot keys, secondary indexes across shards, object storage, search indexes and the specialised stores.05Distributed Systems EssentialsPartial failure, CAP and PACELC, consistency models, quorums, clocks, consensus, distributed transactions, idempotency and CRDTs: the ideas behind every "what happens when this node dies?" question, each with a small model you can run.06Messaging and Async ProcessingQueues, logs and pub/sub at the design level: what each buys you, how ordering, retries and overload behave, and how events, streams and scheduled jobs fit into a system.07APIs and Real-Time CommunicationHow the boxes talk: writing the API section, pagination, REST vs GraphQL vs gRPC, pushing data with polling, SSE and WebSockets, scaling connection servers, webhooks, rate limiting, idempotency keys and versioning.08Building Blocks: IDs, Hashing and Probabilistic StructuresThe small parts that case studies keep reaching for: unique IDs, short codes, Bloom filters, HyperLogLog, count-min sketches, geohashes, quadtrees, tries and Merkle trees, each as a model you can run and defend.09Reliability, Security and OperationsDesigning for the bad day: limiting blast radius, surviving slow and failing dependencies, degrading gracefully, seeing what is happening, shipping safely, recovering data, and the security questions every design review asks.10Case Studies: Core ServicesSix classic backend prompts worked end to end, each in the same shape from requirements to trade-offs, with the numbers that drive every decision calculated and the core mechanism built as a model you can run.11Case Studies: Social and Real-TimeFive designs where many people read and write the same things at once — a news feed, chat, search autocomplete, likes and comments, and a leaderboard — each worked from requirements to trade-offs, with the numbers that decide it computed in code.12Case Studies: Media, Location and MoneySix full case studies, each in the 45-minute shape: video streaming, file sync, ride-hailing, nearby search, payments and ticket booking, with the numbers that drive every decision calculated in code.13Frontend System Design: FoundationsThe frontend round from requirements to optimisations: rendering strategies, component and state architecture, client caching, virtual lists, real-time updates, Core Web Vitals, loading, offline, accessibility, security and micro-frontends, with the logic run in Node and the numbers calculated.14Frontend Case StudiesEight frontend system design rounds worked end to end (autocomplete, news feed, carousel, chat, collaborative editor, product page and checkout, data table, design system), each with the logic at its heart run in Node, the numbers calculated, and the trade-offs you say out loud.15Review QuestionsRapid revision before an interview: short questions with model answers you can say out loud in a minute, each linked to the topic that explains it in depth.
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