Design an ads event reporting system

Design an ads event reporting system that collects user-ad interaction events and serves aggregated metrics.

Requirements

1. Ingest events from multiple platforms (web/mobile/server):
   • impression , click , conversion (extendable to more event types)
2. Event schema includes at minimum:
   • event_id (unique), timestamp (event time), ingest_time , user_id (or anonymized id), ad_id , campaign_id , event_type , plus optional attributes (geo, device, app version).
3. Reporting queries :
   • Time-series aggregates (e.g., per minute/hour/day)
   • Group-by dimensions: campaign/ad, geo, device
   • User cohort / segment partitioning (e.g., users grouped by country, or an offline-defined cohort id)
4. Correctness and reliability :
   • Handle duplicates (retries), out-of-order and late events
   • Support backfills and reprocessing
5. Latency goals (assume):
   • Near-real-time dashboards (e.g., p95 < 1–5 minutes)
   • Accurate daily finalized reports
6. Scale goals (assume):
   • 50k–500k events/sec peak
   • Store raw events for 30–90 days; aggregates longer

Deliverables

Propose an end-to-end architecture, storage layout/partitioning, aggregation strategy, APIs for querying, and how you ensure deduplication + correctness with late events. Include key tradeoffs.