System design interviews are the most feared round in senior engineering interviews — and for good reason. There’s no single “correct” answer, the scope is enormous, and interviewers are evaluating you on dimensions you might not even realize.
This crash course breaks down everything you need to know, from the fundamentals to full system designs.
What You’ll Learn
Foundation & Core Concepts (early lessons): Understand what interviewers actually evaluate, learn a repeatable framework for structuring your answer, master back-of-envelope estimation, and build the core toolbox — networking and protocols, API design, databases (indexing, ACID, isolation), and common components.
Scalability & Distributed Systems: Go deep on the ideas every senior interview probes — how to scale reads (caching tiers, read replicas, CDNs, denormalization/CQRS), how to scale writes (sharding, partitioning, write buffering), replication and the consistency spectrum (leader–follower, quorums with W + R > N, CAP), the pitfalls that break systems at scale (hot keys, cache stampedes, cascading failure, back-pressure), plus consensus & coordination (Raft, leader election, distributed locks), distributed transactions (2PC, saga, outbox), and stream processing (Kafka/Flink, windowing, lambda vs kappa).
Reusable Patterns & Tools: The building blocks that recur across designs — real-time updates (polling vs SSE vs WebSocket, pub/sub fan-out), dealing with contention (optimistic vs pessimistic locking, idempotency), handling large blobs (presigned URLs, chunking, CDN), managing long-running tasks (job queues, workers, webhooks), plus a data modeling lesson and a key-technologies decision guide (which database/queue/store to reach for, and why).
Real System Designs: Walk through 27 classic system design problems end-to-end — chat, video streaming, ride-sharing, search, e-commerce, payments, distributed cache, rate limiter, web crawler, news feed (fan-out), URL shortener, notifications, typeahead, unique ID generation, a Dynamo-style key-value store, a distributed message queue, file sync (Google Drive/Dropbox), an ad-click aggregator, a collaborative editor (Google Docs), Yelp (geo search), Ticketmaster (booking), a flash-sale system, top-K / trending, metrics & monitoring, a distributed job scheduler, live comments, and an online auction. Each follows a consistent structure: requirements gathering, API design, high-level architecture, and deep dives into the hard problems.
Advanced Topics: Specialised building blocks that senior designs lean on — proximity search (geohash/S2/quadtrees), data structures for big data (Bloom filters, HyperLogLog, Count-Min sketch), time-series databases, vector databases (ANN, embeddings, RAG), and change data capture (keeping caches, search and warehouses in sync).
In the Wild: Five real-company case studies — how Discord stores trillions of messages, Figma does multiplayer editing, Shopify survives flash sales, Slack runs its job queue, and Spotify delivers hundreds of billions of events a day — each showing the textbook patterns as they look in production.
Interview Mastery (final lessons): Learn the common mistakes that sink candidates and walk through a complete mock interview to see the framework in action. A dedicated How to Prepare lesson lays out a four-week study plan.
Who This Is For
- Software engineers preparing for senior/staff-level interviews at top tech companies
- Engineers who can code but struggle with open-ended design questions
- Anyone who wants to build a systematic approach to system design
Prerequisites
- Basic understanding of web applications (HTTP, REST APIs, databases)
- Familiarity with at least one programming language
- Some experience building or working on backend systems
Let’s get started.