Doordash System Design Interview

Rundown:

• Quick intro
• Exercise
• Q/A

The exercise

In 6 months from now, DoorDash is going to sponsor a charity event by releasing a new app that allows people to make a donation to one of 10 charities. (This donation app has nothing to do with DoorDash or food). Assume we already developed the iOS, Android and web UI frontends. The UI has a form which contains fields for first name, email, payment card info, a way to pick a charity, a dollar amount and a big donate button on the bottom. The app will only really be used once because the charity event starts on and will only be online that Friday - Sunday. During those 3 days, 10m donations are expected. We estimate we might collect $100m in donations for the 10 charities we are working with. We negotiated with a 3rd party payment provider called Braintree Payments API who's got a very simple REST API - you POST the payment card info to their endpoint and they return a 201 created response. We really want to use them because they are giving us a nice low transaction fee for each donation since this is a special event for non profits. The application does not need to disburse money into the 10 non-profit bank accounts. After the event, we will go ahead and total up the amount donated for each charity and CFO will manually write the check

My thoughts

• I felt I clarified my requirements well but interviewer and I focused on getting the payment stuff wired up as well as supporting notification to user on successful donation. We didn't worry too much on the "charity should see how much they raised" considering that the problem statement is that the donation website is up for only a few days and CFO will write the check to the charity with the donation amount (only 10 charities!)

• Interviwer and I focused on points of failure and had a discussion on what I'd do to mitigate.

• Interviewer was really nice and I think he was helpful when needed. Fingers crossed I did enough to pass. Market tough and I need job