← Early-stage Startup Interview Insights
Spent the first 15 minutes just figuring out the schema before writing a single line of code, which was probably the right call but felt slow in the moment.
Start by clarifying functional and non-functional requirements, then design a high-level architecture with core entities and APIs. Dive into data modeling for trains, routes, schedules, and bookings, and discuss concurrency and consistency for seat booking. Optionally cover cancellation/refund flow and scalability considerations.
Pro tip: Emphasize idempotency and transactional integrity in booking APIs to prevent double-booking, and discuss how you'd handle race conditions with database locks or optimistic concurrency control.
Ask about scale (users, trains, bookings per day), read/write ratio, consistency needs, and whether cancellations/refunds are in scope. Define core use cases and constraints.
Outline main components: API gateway, booking service, search service, payment service, and databases. Sketch API endpoints for search, availability, booking, and cancellation.
Design schemas for stations, trains, routes, schedules, seats, bookings, and payments. Consider indexing for search and availability queries.
Explain how to handle seat locking, transactions, and idempotency to avoid double-booking. Discuss isolation levels and failure handling.
Describe the cancellation flow, refund policies, and how to update seat availability and payment status atomically.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the core entities and their relationships: trains, routes, stations, schedules, seats, and bookings. Then propose a normalized schema with appropriate keys and constraints, and discuss trade-offs like denormalization for read performance and handling concurrency for seat reservations.
Pro tip: Emphasize that seat availability should be derived from bookings rather than stored as a mutable count, to avoid race conditions and ensure consistency. Also, mention that for an early-stage startup, you'd start with a simple normalized schema and only denormalize when performance metrics demand it.
Ask about scale, read/write patterns, and whether routes are fixed or dynamic. State assumptions like daily trains, seat classes, and booking lifecycle.
List entities: Train, Route, Station, Schedule, Seat, Booking, Passenger. Define relationships: a route has many stations, a schedule has many seats, a booking references a schedule and seats.
Propose tables with primary keys, foreign keys, and indexes. For example: trains(id, name), routes(id, train_id, origin_station_id, destination_station_id, departure_time, arrival_time), seats(id, train_id, seat_number, class), bookings(id, user_id, schedule_id, status, created_at), booking_seats(booking_id, seat_id).
Discuss how to prevent double-booking: use transactions with SELECT FOR UPDATE or unique constraints on (schedule_id, seat_id) in booking_seats. Mention optimistic vs pessimistic locking.
Talk about normalization vs denormalization for read-heavy workloads, caching seat availability, and sharding by route or date if needed.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Talked through REST endpoints, explained why I kept search and booking separate.
Start by clarifying the core booking flow and constraints (e.g., double-booking prevention, concurrency, early-stage speed vs. correctness). Then walk through your API design choices—resource modeling, endpoints, idempotency, error handling—and explicitly tie each choice to trade-offs relevant to a startup (e.g., simplicity, scalability, developer velocity).
Pro tip: Show you think about failure modes and idempotency upfront—mention how you'd handle duplicate booking requests and race conditions, since that's where most booking APIs break in production.
Ask about expected scale, concurrency, and whether the system needs to support real-time availability or can tolerate eventual consistency. This shows you design based on context, not dogma.
Model the domain with clear resources (e.g., /bookings, /availability) and use RESTful or RPC-style endpoints. Explain why you chose that style (e.g., REST for simplicity, gRPC for performance).
Describe how you prevent double-booking (e.g., optimistic locking, database constraints, distributed locks) and ensure idempotent booking creation (e.g., idempotency keys).
Outline consistent error responses (e.g., 409 Conflict for double-booking, 400 for invalid input) and how clients should retry or recover. Mention rate limiting and validation.
Explain choices like synchronous vs. asynchronous booking, versioning strategy, and how the API might evolve as the startup scales. Show awareness of simplicity vs. future-proofing.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.