System designHardsd-g120

Subject Distributed transactionsLevel Senior–Staff~55 minCommon in Databases & SQL · Distributed systems interviewsIndustries Technology, Software development

Question

Design the checkout flow for a travel-booking platform where one purchase must reserve a flight (airline API), book a hotel (hotel API), charge the customer (payment service), and issue loyalty points (loyalty service) — four independent services with their own datastores, no shared transaction. If any step fails, the whole booking must unwind cleanly with no orphaned charge or held inventory. Volume ~3,000 bookings/sec. Describe how you coordinate this without a 2PC and how you guarantee consistency and exactly-once effects under retries.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.