System requirements

Functional:

List functional requirements for the system (Ask interviewer if stuck)...

• user can use the system to send a request to book a ticket
• user can see the order status
• user can pay for the ticket
• user can cancel the ticket if they haven't paid for it
• the system can notify the user for the order update or the event update

Non-Functional:

List non-functional requirements for the system...

• availability: the system should have high availability
• scalability: the system should be scalable to support hundreds of millions of users
• reliability: the system should be recovered from the errors
• consistency: the system should support strong consistency for ticket booking

Capacity estimation

Estimate the scale of the system you are going to design...

100 million user

10 million active users: every month book 3 tickets

10*10^6 * 3 / 10 / 10^5 ~ 3 qps

It's not a write heavy system

read Qps: 10*3 = 30

API design

Define what APIs are expected from the system...

• POST: /book (userId, eventId, eventDetails)
• POST: /cancel (userId, orderId)
• POST: /pay (userId, orderId)
• GET: /find (orderId)
• GET: /search (userId, criteria)

Database design

• User Table: userId, name, email, phone
• Oder table: orderId, ticketId, createdTime, status
• Event table: eventId, eventStart, eventEnd, location, company
• Ticket: userId, eventId, seat(optional)

High-level design

• userClient
• Api GateWay
• Booking service
• Ticket Server
• Kafka
• Payment Service
• Notification service

Request flows

Explain how the request flows from end to end in your high level design. Also you could draw a sequence diagram using the diagramming tool to enhance your explanation...

Detailed component design

Dig deeper into 2-3 components and explain in detail how they work. For example, how well does each component scale? Any relevant algorithm or data structure you like to use for a component? Also you could draw a diagram using the diagramming tool to enhance your design...

Trade offs/Tech choices

Explain any trade offs you have made and why you made certain tech choices...

Failure scenarios/bottlenecks

Try to discuss as many failure scenarios/bottlenecks as possible.

Future improvements

What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?