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System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

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This is a medium difficulty System Design question, commonly asked during Technical Screen rounds at Warner Bros Discovery.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Warner Bros Discovery during technical interviews.

Design an ad content delivery system with A/B testing | Warner Bros Discovery Interview Question

Quick Overview

This question evaluates system-design and distributed-systems competency, specifically real-time ad serving, targeting and campaign data modeling, high-throughput event logging, and A/B testing/experimentation infrastructure including experiment assignment and metric computation.

Design an ad content delivery (ad serving) system that selects and serves ads to users, and supports A/B testing / experimentation.

Core scenario

A client (web/mobile app) requests an ad for a placement (e.g., homepage banner). The system must choose an eligible ad and return creative metadata quickly.

Requirements

Functional

Create/manage campaigns and creatives (basic campaign metadata is enough).
Targeting (at least: country/device/app placement; optionally user segments).
Select an ad to serve for each request.
Impression and click tracking.
Basic delivery controls (at least one): pacing/budget, frequency capping, deduplication.
A/B testing : run experiments that change selection/ranking logic or creatives; assign users deterministically to variants; log outcomes.

Non-functional

Very low latency for ad requests (typically tens of milliseconds).
High throughput (can assume millions of requests/day+).
High availability.
Accurate enough reporting (define what must be real-time vs eventually consistent).

Deliverables

High-level architecture and key services.
Data model/storage choices for campaigns, targeting, and events.
Serving path (request → decision → response) including caching.
Event logging pipeline and metrics.
A/B test design: assignment, exposure logging, metric computation, and guardrails.
Key trade-offs and failure modes.

Quick Overview

Requirements

Functional

Create/manage campaigns and creatives (basic campaign metadata is enough).

Targeting (at least: country/device/app placement; optionally user segments).

Select an ad to serve for each request.

Impression and click tracking.

Basic delivery controls (at least one): pacing/budget, frequency capping, deduplication.

A/B testing : run experiments that change selection/ranking logic or creatives; assign users deterministically to variants; log outcomes.

Non-functional

Very low latency for ad requests (typically tens of milliseconds).

High throughput (can assume millions of requests/day+).

High availability.

Accurate enough reporting (define what must be real-time vs eventually consistent).

Deliverables

High-level architecture and key services.

Data model/storage choices for campaigns, targeting, and events.

Serving path (request → decision → response) including caching.

Event logging pipeline and metrics.

A/B test design: assignment, exposure logging, metric computation, and guardrails.

Key trade-offs and failure modes.

Design an ad content delivery system with A/B testing

Quick Overview

Core scenario

Requirements

Functional

Non-functional

Deliverables

Solution

Submit Your Answer to Earn 20XP

Design an ad content delivery system with A/B testing

Quick Overview

Core scenario

Requirements

Functional

Non-functional

Deliverables

Solution

Submit Your Answer to Earn 20XP