Design Webhooks and Metric Aggregation

The interview report described two system design rounds in the same category:

1. Design a webhook delivery platform Build a multi-tenant webhook system for external customers. Internal product services emit business events such as order.created , order.updated , and trip.completed . Customers can register HTTPS endpoints and subscribe to selected event types. The system should:
   • accept event publications from internal services
   • fan out events to subscribed customer endpoints
   • deliver webhooks with low latency
   • support retries with exponential backoff on failures
   • provide at-least-once delivery semantics
   • include payload signing and secret rotation
   • help consumers deduplicate repeated deliveries
   • expose delivery status, logs, and metrics
   • isolate tenants and protect the platform from slow or failing endpoints
   Discuss APIs, storage, queueing, retry strategy, security, observability, and scaling bottlenecks.
2. Design a vehicle metrics aggregation system Build a telemetry platform for a fleet of connected vehicles. Each vehicle sends measurements such as speed, battery level, GPS location, temperature, and health signals every few seconds. The system should:
   • ingest high-volume telemetry from many vehicles
   • store raw events for debugging and historical analysis
   • compute rollups such as per-vehicle 1-minute aggregates and fleet-wide hourly aggregates
   • support dashboards and queries over recent and historical data
   • support alerting for anomalies or threshold violations
   • handle late, duplicated, or out-of-order events
   • support retention and downsampling policies
   Discuss ingestion, stream processing, storage choices, aggregation strategy, query serving, and fault tolerance.