Design a near-real-time weather API

Q: Design a near-real-time weather API

This question evaluates system design competencies such as real-time data ingestion, API design, caching and invalidation, storage modeling and indexing, reliability under upstream slowness, idempotent retries and backfill, rate-limit handling, and observability for freshness SLOs.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Onsite rounds at HubSpot.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at HubSpot during technical interviews.

Question

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

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

Design a near-real-time weather API

Quick Overview

System Design: Weather Data Platform (Onsite)

Context and Assumptions

Requirements

Deliverables

Solution

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