- Back-of-the-Envelope Estimation
The step most candidates skip and most interviewers weight heavily. Powers of two and the latency numbers worth memorising, then the arithmetic that turns "design Airbnb" into concrete QPS, storage and bandwidth figures — worked end to end from real row counts. How to size a cache, when a number tells you the design is wrong, and why being an order of magnitude out is fine but a thousand times out is not.
- System Design Basics – The Parts of a Production System
Every box on the whiteboard, named and justified: DNS, CDN, load balancer, a stateless web tier, cache, primary and replica databases, a message queue, object storage, and the logging and metrics that tell you which one is broken. Built up from a single server to a system that survives real traffic, with the reason each part gets added at the point it stops being optional — plus where a monolith is still the right answer.
- System Design – Where to Start
What system design actually is, why the question has no single right answer, and the four-step framework that keeps an hour from wandering: scope the requirements, estimate the load, sketch a high-level design, then go deep on the part that matters. What an interviewer is really scoring, the mistakes that sink candidates who know the material, and how the rest of this track is ordered.
- Frontend Dev – Build Tooling and Deployment
What happens between your source and the files a browser downloads, and how those files get somewhere real. Bundling, the dev server, environment variables and why they are not secret, static hosting on a CDN, cache headers and content hashing, the SPA fallback that 404s every deep link if you forget it, and a CI pipeline worth having.
- Frontend Dev – Testing
How you change code you did not write without being afraid. What is worth testing in a UI and what is not, testing what the user sees rather than what the component holds, querying by role so a test breaks when the app breaks and not when a class name changes, and where end-to-end tests earn their keep.