Design flight-price search service

Q: Design flight-price search service

This question evaluates a candidate's proficiency in system design, distributed backend architecture, data modeling, real-time provider integration, and operational concerns for building a scalable, cost-efficient flight price search service.

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 Take-home Project rounds at Circle.

Q: What role is this question designed for?

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

Question

System Design: Cheapest Flight Search Across Multiple Providers

Context

Design a backend system that searches multiple flight providers (airlines, OTAs, GDS/aggregators) to return the cheapest flight tickets for users. The system must handle a high volume of queries, volatile prices, and frequent updates while remaining scalable and cost-efficient.

Requirements

Inputs: origin, destination, departure date(s), return date(s), cabin class, number of stops.
Date flexibility: exact dates or flexible windows (e.g., ±3 days) and calendar view.
Core outputs: list of itineraries/offers sorted by price with filters, plus a fast “cheapest per day” calendar.
System concerns to describe:
1. High-level architecture: ingestion from providers, normalization, deduplication, search index.
2. APIs: search, quote/validate (re-price), and ancillary endpoints.
3. Caching strategy.
4. Data freshness and update propagation.
5. Rate limiting, retries, and resilience patterns.
6. Consistency vs availability trade-offs.
7. Scalability and cost-control strategies.
8. Schemas and indexes that enable fast queries and rapid price updates.

Design flight-price search service

Quick Overview

System Design: Cheapest Flight Search Across Multiple Providers

Context

Requirements

Solution

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