Design ads frequency capping service
NetflixSoftware Engineer · Onsite
Last updated
This question evaluates a candidate's ability to design a low-latency, high-QPS, multi-tenant frequency capping service, testing competencies in identity resolution, hierarchical cap modeling, window semantics, counter and storage architecture, consistency versus latency trade-offs, real-time decisioning APIs, configuration/versioning, backfill, reporting, privacy/compliance, and failure handling. It is commonly asked to assess systems-design proficiency in distributed systems, databases, caching, API design, and operational reliability; it belongs to the System Design domain and emphasizes practical application with system-level conceptual reasoning rather than purely algorithmic detail.
Design an ads frequency capping service that limits how many times a user sees a creative or campaign within configurable time windows (e.g., 3/day per campaign, 10/week advertiser-wide). Compare it to a generic rate limiter and explain the extra components required for advertiser configuration and onboarding. Cover: identity resolution (cookies, device graph, logged-in IDs), cap dimensions (creative/ad group/campaign/advertiser), window semantics (sliding vs tumbling), counter and storage design, consistency vs latency trade-offs, real-time decisioning at high QPS, configuration APIs and validation, config propagation/versioning and rollback, backfill/migrations, reporting needs, privacy/compliance, and failure handling.
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