System Design: Weather Data Platform (Onsite)

Context and Assumptions

• You are designing a service that pulls best-effort hourly weather data from an external Weather Service API for ~2,000 locations (e.g., city IDs or lat/lon).
• "Current temperature" is defined as the latest available hourly observation (e.g., the reading for the hour starting at HH:00Z). The platform must ingest each new hourly dump quickly enough so clients see data no more than 10 minutes stale relative to now.

Requirements

• Data served must be at most 10 minutes stale.
• Handle upstream API slowness, partial failures, and outages gracefully.
• Support retries, idempotent ingestion, and backfill for missed hours.
• Respect provider rate limits.
• Provide monitoring/alerting on freshness SLOs.
• Support horizontal scale for traffic spikes on the read API.

Deliverables

1. High-level architecture (ingestion, storage, cache, API, scheduler).
2. API design (e.g., GET /temperature?locationId=..., response schema, error and freshness metadata).
3. Data model and storage choices (including TTL/indexing strategies).
4. Caching and invalidation plan to meet the 10-minute freshness.
5. Deployment, cost, and security considerations.
6. Test and observability strategy.