Stop 20 · Interview PreparationTechnical · 4/8

System design (full-stack)

Part of the Full Stack Developer Roadmap

In short

"Design live order tracking for a food app." A full stack design round wants the whole picture: what the screen shows, how it gets data, what the API looks like and where data lives.

Higher-level interview questions about architecting a complete feature or app — spanning frontend rendering strategy, API design, and backend data modeling together.

The purple blob in a hard hat studies a cardboard model of a metro station on a table.

Think of it like this

Planning a new metro station

Engineers first ask how many people use it at rush hour, where they enter, and which platforms they need. Only then do they draw escalators and gates. Design rounds reward the same order: needs and numbers first, boxes later.

Watch it happen

A 40-minute design round, in order

Requirements

Estimates

Frontend

API

Data

Scale

1/6Ask: who uses it, what must they see, how fresh must it be? Agree on 3 to 5 core features.

The big ideas

What you need to know

Clarify before you draw

Spend the first five minutes on questions. A wrong assumption early wastes the whole round.

Numbers guide choices

Rough estimates tell you whether polling is fine or you need push, and whether one database is enough.

Cover every layer

Rendering choice, API shape, data model, caching and real-time. Full stack rounds expect all of them briefly.

Say the trade-offs

For each choice, name what you gave up. "SSE is simpler than WebSockets, but only server to client."

See it in code

Walk through the code

1// Live order tracking: write the contract before drawing boxes2type OrderStatus = "PLACED" | "ACCEPTED" | "PREPARING" | "PICKED_UP" | "DELIVERED";3 4// REST, first load of the tracking page: GET /api/orders/:id5interface OrderView {6  id: string;7  status: OrderStatus;8  items: { name: string; qty: number }[];9  rider?: { name: string; lat: number; lng: number };10  etaMinutes: number;11}12 13// Push, after that: small events over WebSocket or SSE14type OrderEvent =15  | { type: "status"; status: OrderStatus }16  | { type: "rider_location"; lat: number; lng: number };

1/3A clear status enum. The UI, API and database all share these exact values.

Putting the contract on the whiteboard shows the interviewer exactly what moves between browser and server, and keeps the rest of the design grounded.

Save yourself the pain

Common mistakes

Oops

Jumping straight to Kafka, microservices and Kubernetes.

Do this instead

Start with the simplest design that meets the numbers, then scale the part that actually breaks.

Oops

Designing only the backend in a full stack round.

Do this instead

Cover the screen, rendering choice and client state too. That's what makes it full stack.

Your mission

Run a mock design round

~45 min

Quick check

Rider locations update every few seconds for thousands of active orders. Where is the best place to keep them?

Go deeper

1Practice a mock full-stack system design question, e.g. 'design a Twitter-like feed'.
2Structure your answer across all layers: frontend, API, backend, database.
3Study how a real product you use is likely architected end-to-end.

More technical at this stop