System designHardsd-g521

Subject Pub subLevel Senior–Staff~45 minCommon in Distributed systems interviewsIndustries Technology, Software development

Question

Design a content-based / topic pub-sub broker that supports hierarchical topics and wildcard subscriptions (e.g. sensors/+/temperature, orders/us/#) plus attribute filters (price > 100 AND region = 'eu'). Scale: 5M active subscriptions, 1M messages/sec, and a single message may match thousands of subscriptions. Matching must be fast enough not to bottleneck publish throughput, and subscriptions change frequently.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.