Ad Click Aggregation / Ad Server — Simple

Problem statement (interviewer prompt)

Design a real-time ad-click aggregation system. Ingest billions of click events/day, dedupe + validate (fraud), aggregate per advertiser + campaign + time bucket for billing and dashboards, and support both real-time (seconds) and end-of-day batch reconciliation.

flowchart LR
  U([User])
  ADS[Ad Server]
  AUC[Auction / Bidder]
  CLK[Click / Impression event]
  K[[Kafka]]
  AGG[[Stream Aggregator]]
  RPT[(Reports)]
  U --> ADS --> AUC
  U --> CLK --> K --> AGG --> RPT

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class U client;
    class ADS,AUC,CLK service;
    class RPT datastore;
    class K,AGG queue;