How to solve the Facebook iOS App Design Interview — Amazon Engineer perspective

Last week, a reader contacted me to explain issues he was facing in his recent interview with Facebook. During the System Design challenge, he was asked to design a Mobile Application. Unlike the traditional System Design interview, this one focuses specifically on the architecture of the mobile application, and then moves into its many different details.

Since that reader has been part of a mobile application team, and his view point was rather limited, he did not have enough exposure to fully plan an application, and to help him prepare for such an interview. That’s why we’re going to explore exactly that in this article.

Clarification

When sitting in an interview and being asked to “design Instagram”, it’s the first and most crucial step to ask clarifying questions. What part of the app do we need to concentrate on? We can’t possibly design the whole application within 20 minutes — typically the amount of time dedicated for the actual design part. The remainder is reserved for questions from the interviewers, as well as yours.

Typically, interviewers want you to concentrate on a challenging and complex part of the application, like the “news feed”, or the “instant chat”.

A few examples of clarifying questions are:

• What part of the app should I design? Authentication? Feed? User profiles? Messaging? Post comments? Application nowadays…