What Does a Systems Design Question Look Like?
It's pretty easy to tell when you're getting a systems design question during an inteview-- most interviewers will start off with a high level overview of an application or service. They might ask how familiar you are with it, and will then ask you to design it.
Here are some sample questions:
- How would you build Google Analytics?
- Choose a web application that you use and walk me through its moving parts.
- How would you design Instagram/Yelp/Youtube/Facebook?
- Why do you think X framework fits better than Y framework on this application?
- Suppose we want to build a ticketing system. How do we handle X, Y, Z..?
- If your web app failed to give responses, how do you find out what happened, and how do you plan to fix the issue?
- We want to design a service that does X.
Beyond testing your knowledge of technical concepts, trade-offs, identifying bottlenecks, and thoughts on maintainability, interviewers are also looking to see how well you understand and clarify requirements.
Hence why questions like "How would you build Google Analytics?" are less frequent than "Suppose we wanted to build an analytics service..." Interviewers are vague on purpose, and are expecting to hear questions like:
- What are the use cases? What are we trying to build here? Let's say we're building a CMS to help bloggers edit their content. Will it only be bloggers using the application, or could it be illustrators, marketing folks, and operations people that will also have their own needs?
- How long do we need to store data for? Identifying the data store that we'll be using (in-memory vs. on-disk, NoSQL vs. SQL, columnar vs. time-series, etc.) is dependent on a multitude of factors, one of which is the length of time we'll need to store information.
- What is the scale of the metrics we'll be getting? (What's our database strategy?)
- Does there need to be a web client? (Do we need to design components?)
- What should the user interaction be? (Do we want MVC on the frontend?)
- How up to date should the metrics be?
- Do we want to expose logs? (For maintainability)
As far as the actual "solution", interviewers are usually looking for some sort of diagram of all the moving parts of the system that looks like this:
You usually have 45 minutes to an hour to get a working solution on a whiteboard.