Case Studies

How well-known products combine the primitives—end to end, with napkin math and architecture you can retell under pressure. For fundamentals through staff-level theory, interview frameworks, and structured case studies, start with SysDesign Core. Also see How would you Design? for interview-style architecture prompts.

SysDesign Core — full curriculum

Capstone track: fundamentals, databases, caching, distributed systems, interview frameworks, and eight canonical case studies with trade-off analysis.

13 chapters
SysDesign Core

First principles to staff level: CAP, sharding, messaging, RADIO interview framework, patterns library, and cheat sheets—learning and interview tracks.

Guide
How Reddit works

You’ll explain how feeds, voting, and comment trees scale—and which loop fails first when traffic spikes.
Guide
How Slack works

You’ll diagram live channels, fan-out, and search—and defend WebSocket vs polling when latency matters.
Guide
How Spotify works

You’ll trace audio from catalog to CDN to playback—and see where rights, offline mode, and recommendations plug in.
Guide
How Apache Kafka works

You’ll choose partitions, replication, and consumer groups—and explain what breaks when a broker goes down.
Guide
How the X (Twitter) timeline works

You’ll compare fan-out on write vs read, celebrity timelines, and why hydrating a tweet is its own scaling problem.
Guide
How Google Docs works

You’ll compare OT and CRDT, sketch revision storage, and argue permissions without blocking concurrent edits.
Guide
How Airbnb works

You’ll walk a booking from search to payment—and point to where double-booking is actually prevented.
Guide
How the ChatGPT app works

You’ll budget inference, sketch streaming with RAG and tools, and name the knobs for latency, cost, and safety.
Guide
How WhatsApp-style chat works

You’ll trace a message from send to delivered tick—ordering, storage, E2EE paths, and media at high concurrency.
Guide
How YouTube works

You’ll follow an upload through transcode and CDN—and estimate storage, egress, and two-stage recommendation cost.
Guide
How Uber works

You’ll design geo matching, surge, and trip state—and talk through broker failure without hand-waving.