Design a distributed ad campaign delivery & budget pacing system
PremiumBackend systemHard
- Real time serving
- Distributed counting
- Budget pacing
Quick answer
This backend system interview question asks you to design a distributed ad campaign delivery & budget pacing system. 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 distributed Ad Campaign Delivery and Budget Pacing platform. Advertisers create campaigns defining target audiences, creatives, and daily budgets. The system must evaluate incoming ad requests in real-time, select the optimal ad, and track impression events. Crucially, the platform must algorithmically pace ad delivery to spend the budget evenly across a 24-hour period and enforce strict spending limits to prevent overcharging advertisers in a highly concurrent environment.
What must a distributed ad campaign delivery & budget pacing system do?
- Ad Serving: Evaluate incoming ad requests against active campaign targeting rules (e.g., location, device type) and return an eligible ad.
- Budget Pacing: Dynamically throttle or adjust the probability of a campaign winning an auction so its budget is spent smoothly over the day.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Real time serving
- Distributed counting
- Budget pacing
- Stream processing
- Low latency
- Financial consistency
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 distributed ad campaign delivery & budget pacing system 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