What is a system design interview?
System design interview questions are asked to understand how a candidate thinks about complex problems, how well they communicate their ideas, and how well they collaborate with others.
The questions asked in system design interviews are based on large-scale real-world problems. Answering these questions demonstrates the candidate's ability to think creatively and work in a team.
Why is a system design interview important?
The purpose of a system design interview is to assess your ability to design and implement a system from start to finish. System design interview allows you to demonstrate your knowledge, your problem-solving skills, your ability to take a problem and break it down into smaller parts, and your ability to work in a team.
How to prepare for system design interviews?
- The best way to get the most out of your preparation is by practicing.
- Read books and online courses on system design interviews.
- Practice with friends and colleagues.
- Practice with a mentor; it may be an experienced developer or senior engineer on your team or someone else who can give you feedback about what you got right or wrong in a mock interview session and help you improve for your next interview.
- Practice mock interviews using one of the many resources available online.
- To ensure you don't forget what you have learned, keep track of everything in a notebook or spreadsheet and review it regularly.
How to answer a system design question?
System design interview questions focus on abstract problem-solving rather than your specific knowledge of a programming language or technology stack. As such, they're good indicators of how well you can design and solve large-scale problems without having all the information in front of you.
The key to answering system design interview questions is understanding the big picture of how your system works.
When you're asked about the design of a particular system, take time to understand what the interviewer wants to know about this system and why it's important for them.
How do you get started on a system design interview question?
Here is a 7-step process that helps you create a solution to a system design problem:
Step 1: Requirements clarification
When you are asked to design a system for a problem, the first thing that you should do is understand the problem. You need to understand what the users of your system will do, what they are trying to accomplish, and how does your solution help them achieve their goals? Understand all of the constraints of the system. You need to know things like, how many users are there in total? Will they all use the system at once, or will they access it individually?
Step 2: Back-of-the-envelope estimation
It is always a good idea to estimate the scale of the system you are going to design. This will also help later when you focus on scaling, partitioning, load balancing, and caching.
Step 3: System interface definition
Define what APIs are expected from the system. This will establish the exact contract expected from the system and ensure that you haven't gotten any requirements wrong.
Step 4: Defining the data model
Defining the data model will clarify how data will flow between different system components. Later, it will guide for data partitioning and management.
Step 5: High-level design
Draw a block diagram with 5–6 boxes representing the core components of our system. You should identify enough components that are needed to solve the actual problem from start to end.
Step 6: Detailed design Dig deeper into two or three major components; the interviewer's feedback should always guide you to what parts of the system need further discussion. You should present different approaches, their pros and cons, and explain why you will prefer one approach over the other.
Step 7: Identifying and resolving bottlenecks Try to discuss as many bottlenecks as possible and different approaches to mitigate them.
Topics to prepare for system design interview
Here are some of the key concepts you should be familiar with before the system design interview:
- Data partitioning techniques
- Load balancing
- Performance measurement of scalable systems
- API design
- Scalability, availability, and reliability of large systems
- Forward and reverse proxies.
- SQL vs. NoSQL
Top system design interview questions for software developers
Because system design interviews can cover a wide range of topics, it's important to prepare by researching potential questions beforehand.
Here are some of the most common questions asked during a system design interview:
- Design a global file storage and sharing service like Dropbox or Google Drive.
- Design a social network like Facebook, Instagram, or Twitter.
- Design a global chat service like Facebook Messenger or WhatsApp.
- Design a global video streaming service like YouTube or Netflix.
- Design a ride-hailing service like Uber or Lyft.
- Design a web crawler.
- Design Typeahead search.
- Design Ticketmaster.
- Design a key-value store.
- Design an API rate limiter.
- Design URL shortening service.
- Design a distributed messaging system.
- Design an elevator system.
- Design a parking lot system.
- Design a game of chess.
- Design a movie ticket booking system.
- Design a library management system.
- Design an e-commerce store like Amazon.
Common problems during a system design interview
- Don't be afraid to ask questions. It's important to remember that you should always feel comfortable asking the interviewers any question you may have. This is an opportunity for you to get clarification on anything that's unclear or confusing, and it will also help set up a flow of communication between yourself and your interviewer(s).
- Don't be intimidated by the interviewer(s). Several interviewees feel nervous about being put on the spot. If this happens to you, remember that it is part of the process: everyone gets butterflies before an interview! Try not to let nerves get in your way when answering questions - instead, focus on giving great responses.
- Don't be afraid to ask for clarification if something isn't clear enough in terms of what exactly is being asked. Ask questions about requirements and constraints. Questions like what types of data do we need? How much data are we expecting? Where does this data come from? What do we know about our users' behavior (and what don't we know)?
Ready to ace your next tech interview?
In this article, we have discussed the process of system design interviews for software developers. Take a look at Grokking the System Design Interview for system design interview questions like:
- Designing a file-sharing service like Google Drive or Dropbox.
- Designing a popular messaging service like Facebook Messenger.
- Designing popular social network sites like Twitter or Facebook.
- Designing a global video streaming service like YouTube.
- Designing a global ride-hailing service like Uber.
To learn software architecture and practice advanced system design interview questions take a look at Grokking the Advanced System Design Interview.
Read more about system design and coding interviews:
 Top LeetCode Patterns for FAANG Coding Interviews
 System Design Interviews: What distinguishes you from others?