What to Expect in the Deliveroo System Design Interview

Deliveroo calls this round the architecture interview, and it runs 60 minutes. The published guides give the timings: about 5 minutes of introduction, about 45 minutes of design, then 5 to 10 minutes for questions. You draw on a shared whiteboard, and the guides suggest practicing with draw.io or Excalidraw.

For backend roles the interviewer grades design skill, production readiness, scalability, and how clearly you state trade-offs. The questions are open ended rather than scripted, and one question reported on Glassdoor asks you to design a campaign that gives away six million free burgers in 10 minutes.

The Format

The round is a conversation rather than a presentation, and the infrastructure guide describes it as large scale systems design from the infrastructure perspective. The mobile and frontend guides replace that with design work on interface mockups you are given. Across every discipline the guides grade your reasoning and your communication, not the neatness of a finished diagram.

The Question Types

A reported traffic spike question. The free burger campaign appears on Glassdoor more than once, and the reported constraints are specific. Users are already signed in, payment and delivery are out of scope, and each account may claim one burger. The design work therefore covers throttling traffic, locking stock, queueing claims, and preventing a second claim.

Problems from the business itself. Deliveroo's own systems are the obvious source of material, including order placement, dispatch to riders, live order tracking, arrival time estimates, and search over nearby restaurants. These topics are not confirmed as asked questions, but they are the problems the company solves daily, so they are worth preparing.

Interface design for frontend and mobile roles. The frontend guide names production ready interfaces, accessibility, browsers, security, and performance as the graded areas. Accessibility means the interface works with screen readers and with a keyboard alone. One iOS candidate reported designing a rider delivery flow from screens the interviewer supplied, including the end to end flow and the API responses.

A Walkthrough: The Free Burger Campaign

Step 1: Requirements, about 5 minutes. Six million claims inside 10 minutes, one per account, with no payment and no delivery in scope. That averages about 10,000 claims per second, and traffic in the opening seconds is far higher than the average.

Step 2: Protect the entry point. Place a content delivery network and a rate limiter in front of the service, where a rate limiter rejects requests above a set rate for each account and region. Return a clear sold out response instead of a timeout.

Step 3: Count the stock in memory. Keep the remaining count in a fast store such as Redis and decrement it atomically. Atomic means only one request changes the value at a time, so two accounts cannot take the same last burger.

Step 4: Enforce one claim per account. Record each account identifier in a set with a unique key, and reject every duplicate. This check must pass before you confirm the decrement.

Step 5: Make the write path asynchronous. The request returns as soon as the fast store confirms the claim, and a background worker then reads the queue and writes the voucher into the durable database.

Step 6: Plan the failures. Decide what happens when the queue grows, when the cache node fails, and when a client retries the same claim. Giving away 100 extra burgers costs less than a page that stops responding, so say which error you prefer and why.

What the Interviewer Grades

Requirements come first, so ask about traffic, edge cases, and the production limits before you draw anything. State each trade-off out loud, because the backend guide tells candidates to explain their reasoning and their trade-offs. Cover the production concerns that follow a launch, including monitoring, alerts, gradual rollout, and recovery.

Estimate load with real arithmetic, because the numbers decide whether a logistics design works. Keep talking while you draw, and ask whether the interviewer wants more depth or more breadth.

Common Mistakes in This Round

• Designing for the average rate. A 10 minute campaign is defined by its opening spike, so a design that handles only the average rate fails the question.
• Skipping the one per account rule. Duplicate claims are the core difficulty here, and the rule is stated in the question itself.
• Giving no numbers at all. Without a load estimate you cannot justify a cache, a queue, or a database split across machines.
• Treating delivery as a simple map problem. Preparation time, rider supply, and traffic matter more in the real design than routing does.
• Drawing in silence. The round grades your reasoning, so reasoning you never say out loud cannot be graded.

How to Prepare

• Learn the building blocks. Grokking the System Design Interview covers the rate limiters, caches, and queues this walkthrough uses.
• Go deeper on failure handling. Advanced System Design Interview, Volume II covers replication, partitioning, and recovery under spike traffic.
• Rehearse the six steps out loud. Give yourself 40 minutes on a blank whiteboard, because the real round allows about 45.
• See which stage this round belongs to. It is one of two or three interviews in the Deliveroo interview process, next to the motivation question, and the waits are described in how long it takes to hear back.