End-to-End Design

Design a system that records ad clicks and gives advertisers near-real-time aggregates — clicks per campaign, sliced by country or device, over a time window — while also feeding the numbers that go on an advertiser's bill.

In scope: ingesting click events, aggregating them into windowed counts, and serving those aggregates to dashboards and a billing job. Click attribution modeling, fraud and invalid-click filtering, and the ad-serving decision itself are separate systems and out of scope.