Design a stock broking order service
PremiumBackend systemHard
- Order management system
- Exchange gateway
- Idempotency
Quick answer
This backend system interview question asks you to design a stock broking order service. Aim for a design that meets its requirements at the stated scale, then explain its main components, data flow and trade-offs. Interviewers want to see how you scope the problem, size it and defend each choice.
The problem
Design a stock broking order service for a retail trading app: users place buy and sell orders, the broker checks funds and routes them to the stock exchange, and the app shows order status, positions and holdings. The hard part is 20 million orders a day, exchange callbacks that arrive late or twice, and books that must match the exchange.
The broker does not match orders; the exchange does. You own everything between the user tapping Buy and the trade showing in their portfolio.
What must a stock broking order service do?
- Place and manage orders: Users place market or limit buy and sell orders, and can modify or cancel open ones.
- Live order status: Users see each order move through pending, open, partially filled, filled, cancelled or rejected within 1 second of the exchange update.
How well must it do it?
- Correct books: No order is sent twice, no fill is applied twice and no money is blocked without a matching order.
- Latency: From order request to sent to the exchange takes under 50 ms at p99, including the funds check.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Order management system
- Exchange gateway
- Idempotency
- Reconciliation
- Margin blocking
- Order state machine
How you’ll practise
- Requirements
- Estimate
- API and data
- High-level design
- Deep dives
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any backend system design round.
- Clarifies the requirements before drawing anything
- Uses a few numbers that actually change the design
- Draws a clear path from the client to storage
- Picks storage and caching with reasons, not by habit
- Explains what breaks first under load and how to fix it
- States trade-offs openly instead of claiming a perfect design
Questions people ask about this interview question
- Which design type is this question?
- It is a backend system question. You design a stock broking order service and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Hard. It suits engineers preparing for senior interviews, where you are expected to drive the discussion and go deep on trade-offs.
- What should I cover first?
- Start with the requirements: what the system must do, how well it must do it and which numbers change the design. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team