When you book your tickets with an airline you are required to complete the payment and confirm your reservation. Once the reservation is complete then you can either optionally do a web check-in and confirm your seats or just before your departure do a physical check-in at the airport.
In this problem statement, let's design this web-check in system, where the passenger logs in to the system with the PNR, performs the seat selection and the gets the boarding pass. If the passenger tries to book a seat, already booked and assigned to the other passenger show an error message requesting passenger to re-select the seats.
The problem statement is something to start with, be creative and dive into the product details and add constraints and features you think would be important.
- one seat can be assigned to only one passenger and once assigned the seat cannot be transferred
- assume all 100 people boarding the plane are trying to make a selection of their seat at the same time
- the check-in should be as fast as possible
- when one passenger is booking a seat it should not lead to other passengers waiting
- make your high-level components operate with high availability
- ensure that the data in your system is durable, not matter what happens
- define how your system would behave while scaling-up and scaling-down
- make your system cost-effective and provide a justification for the same
- describe how capacity planning helped you made a good design decision
- think about how other services will interact with your service
- ensure the data in your system is never going in an inconsistent state
- ensure your system is free of deadlocks (if applicable)
- ensure that the throughput of your system is not affected by locking, if it does, state how it would affect
Create a design document of this system/feature stating all critical design decisions, tradeoffs, components, services, and communications. Also specify how your system handles at scale, and what will eventually become a chokepoint.
Do not create unnecessary components, just to make design look complicated. A good design is always simple and elegant. A good way to think about it is if you were to create a spearate process/machine/infra for each component and you will have to code it yourself, would you still do it?
To understand the nuances and internals of this system, build a prototype that
- design a database schema for the airline check-in system
- build a simple interface allowing passenger to
- view available seats
- view unavailable seats
- select a seat of their liking
- upon successful booking, print their boarding pass
- simulate multiple passengers trying to book the same seats and handle the concurrency
This is a recommended tech-stack for building this prototype
| Which | Options |
|---|---|
| Language | Golang, Java, C++ |
| Database | Relational Database - MySQL, PostgreSQL |
These are the common pitfalls that you should keep in mind while you are building this prototype
- have a primary key to your tables otherwise the entire table might get locked
- database locking
- database schema design
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This assignment is part of Arpit's System Design Masterclass - A masterclass that helps you become great at designing scalable, fault-tolerant, and highly available systems.