System requirements
Functional:
List functional requirements for the system (Ask the chat bot for hints if stuck.)...
- user is able to search for events they are interested in
- user is able to see the ticket prices, availability of tickets for each event
- user is able to book ticket by making reservation and paying them
- user is able to see their reservations, modify them or cancel them if possible
- Admin is able to post events and make update to the event
Non-Functional:
List non-functional requirements for the system...
- system need to be able to serve multiple users request concurrently
- system need to keep consistency of making reservations i.e. a spot can only be booked by at most one user
Capacity estimation
Estimate the scale of the system you are going to design...
Traffic
- Assume there are 10 events per day, 1000 tickets per events, with 70% book rate, means 7000 reservations per day, about 0.1 QPS
- 10x people look at the details of event -> 70k per day, about 1QPS
- 100x people search events, about 10 QPS
- peak hour is 10x traffic
Storage
- mostly metadata, assume each reservation is 1kB, 7MB storage of reservation per day.
- Other metadata should also be similar levels,
API design
Define what APIs are expected from the system...
v1
message Event{
eventId, name, type, datetime, duration, location, organization,
}
message User{
userId, type(personal, organization), name, age, email, phone, paymentmethod(only one for simplicity)
}
message AccessControl{
userId, eventId, accessLevel
}
message TicketCategory{
categoryId, eventId, venueId, price, capacity, remaining
}
message Reservation{
reservationId, categoryId, seatId, state[pending, paid, cancelled]
}
queryEvent(request: [name, type, dates, location]) returns list[Event]
getEvent(eventId) returns Event
getTicketCategories(eventId) returns list[TicketCategory]
getTickets(eventId, filter[categories]) returns list[Ticket]
createReservation(Ticket, User) returns Ticket
updateReservation(Ticket, User, newState) returns Ticket
createEvent(Event, User) returns state
updateEvent(Event, User) returns state
Database design
Defining the system data model early on will clarify how data will flow among different components of the system. Also you could draw an ER diagram using the diagramming tool to enhance your design...
Table Venue(
venueId, location, name
)
Table Seat(
seatId, venueId, position, other metadata..
)
Table Event(
eventId, venueId, name, datetime, duration, organization
)
Table EventSeats(
eventId, seatId, openess
)
Table User(
userId, type, other metadata
)
Table Access(
eventId, userId, accessLevel
)
Table TicketCategory(
categoryId, eventId, venueId, price
)
Table Reservation(
reservationId, categoryId, seatId, userId, state [pending, paid, cancelled]
)
Table Transactions(
transId, reservationId, reservationToken(for deduping), ...
)
High-level design
You should identify enough components that are needed to solve the actual problem from end to end. Also remember to draw a block diagram using the diagramming tool to augment your design. If you are unfamiliar with the tool, you can simply describe your design to the chat bot and ask it to generate a starter diagram for you to modify...
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...
As drawn in the flow diagram
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...
There are two key problems to consider:
- Avoid oversell
- Dedup payments
To avoid oversell, one need to resolve the possible conflicts behind two requests trying to make reservations to the same
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?