Top System Design Interview Questions for 2021

Top System Design Interview Questions for 2021
Top System Design Interview Questions for 2021


Coding and system design interviews are frequent—and pretty typical—in Big Tech and high-growth companies. The interviewer will expect you to provide a detailed description of how big-scale distributed systems (such as Twitter, Messenger, Netflix, Uber, and so on) were designed.

This round may be complicated since you must cover all of the subjects and tradeoffs in the allotted period, which seems to be impossible. We don’t want the process to be as intimidating as it sounds for you, so let’s go through how to clear it step by step. Read through for some helpful suggestions for avoiding mistakes as well.

What is System Design?

The process of defining system aspects such as modules, architecture, components, and their interfaces, and data for a system based on the stated requirements is known as system design. It is the process of identifying, creating, and designing systems that meet a company’s or organization’s unique goals and expectations.

Cracking System Design Interviews

There are many approaches to system design interviews, but at the end of the day, you need a technique that consistently:

  • Demonstrates to the interviewer that you have the necessary knowledge.
  • Divides the problem into small stages. 

Let’s take a closer look.

Ask clarifying questions

To begin addressing a system design interview question, ask clarifying questions. You must ensure that you grasp the system’s objectives and needs. This will significantly affect the quality of your design since the value of a system is inextricably linked to how well it achieves the desired goals.

What is the system’s goal?

If you’re requested to design an online bookstore, you should start by gathering more precise information about the bookstore’s objective:

  • What kind of shop is it?
  • Is it aimed at a particular kind of reader (for example, students, business executives, or science fiction fans)?
  • Is it a bookstore that sells physical books, digital, or both?

What is the system’s size?

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Although knowing the system’s objective is a step forward, you won’t have a clear vision for the system unless you define a few additional details, like the necessary scale. A university shop that distributes special-order textbooks to the local campus would have a completely different operation than an internet bookstore that sells millions of volumes globally. Ask questions regarding the scale, such as:

  • How many consumers must use the system service each day? How many transactions are there?
  • What are the performance requirements (for example, latency, throughput, and availability)?
  • How is the system’s demand anticipated to evolve in the future?

Where should we concentrate our efforts?

Once the system’s purpose and scale are apparent, it may be beneficial to discuss with your interviewer where to concentrate your attention throughout the interview.

In the case of the online bookstore, there are many various elements to the system, which you won’t be able to cover every detail in 45 minutes. Therefore, it’s important to narrow the emphasis.

Call out your presumptions

Here’s one more thing to think about as you go through the system’s requirements. Be careful to inform the interviewer whenever you make an assumption that will affect your design approach.

Showing your interviewers how you think, rather than simply the end answer, is an important element of system design interviews. Consequently, you should state your ideas aloud so that the interviewer can follow your reasoning without becoming lost or confused.

Topics to Prepare

Systems are complicated, and when you design one, you are confronted with several roadblocks and entire complexities. Therefore, acquaint yourself with a variety of subjects, including: 

  • Concurrency

Do you know what threads, deadlock, and starvation are? Are you familiar with algorithm parallelisation? Do you grasp the concepts of consistency and coherence?

  • Networking 

Do you have a basic understanding of IPC and TCP/IP? Do you understand the distinction between throughput and latency, and why each is important?

  • Abstraction

You should be familiar with the systems on which you are constructing. Do you have a general understanding of how an operating system, file system, and database work? Do you understand the different layers of caching in a contemporary operating system?

  • Performance in the real world 

You should be aware of the speed of everything your computer is capable of, including the relative performance of RAM, HDD, SSD, and your network.

  • Estimation

Particularly in the form of a back-of-the-envelope calculation, estimation is useful because it allows you to filter the number of potential solutions to just those that are practical. Then you just need to create a few prototypes or micro-benchmarks.

  • Availability and reliability 

Are you considering how things may fail, particularly in a distributed environment? Do you know how to build a system to deal with network outages? Do you understand the concept of durability?

Keep in mind to not aim for mastery of all of these subjects. Just ensure you have a solid understanding of the situation.

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System Design Interview Questions

The system design round has become a regular component of the software engineering interview process. If you want to obtain a dream job at one of the major tech companies (particularly as a senior engineer), you must explain your approach to developing a huge, difficult scalable system.

This is where familiarizing yourself with common system design interview questions come into play. Here are some important questions you may be asked in your next interview.

General System Design Interview Questions

  1. How would you go about creating a TinyURL system?

A TinyURL is a URL service that enables users to input a lengthy URL and get a shorter, unique URL in return. A hiring manager may ask this to give you the chance to demonstrate your strong design background. You may concentrate on fundamentals such as how to generate a unique ID for each URL, manage redirection, and remove expired URLs.

  1. How do you create a large-scale social media platform?

The goal of creating a large social media network like Instagram, Facebook, or Twitter is to create a platform that allows users to see a newsfeed containing postings. The following are the essential characteristics that social media services need:

  • Users have the option of commenting on and liking a post.
  • It should be able to handle many users at the same time.
  • A news feed and recommendation system should be included.
  • Privacy restrictions must also be implemented.
  • Trending posts/tweets should be displayed.

The following tools may be used in the construction of a large social media platform: 

  • Rolling updates and replica nodes to maximize availability
  • A trained machine learning algorithm to suggest articles and news feeds
  • A database schema that stores celebrities and certain users separately
  • A social graph to monitor certain behaviours
  1. How do you build a vending machine in Java? 

You must create code to build a vending machine that sells a variety of goods like chocolates, candies, and cold drinks and accepts various currencies such as nickels, dimes, quarters, and cents. Create a unit test to show that these typical use-cases function.

  1. How does one go about creating a URL shortening service like or

This is another typical system design interview question. You’ve been provided with a (usually) lengthy URL; how would you build a service to produce a shorter and more unique alias for it? If you’re unfamiliar with URL shortener services, check out some of the more popular ones, such as from Google and, which Twitter utilizes.

Be sure to include the database structure and the reasoning behind certain design choices, such as how long you retain the data, how you obtain metrics and analytics, etc. If you are stuck, go to the solution provided in the Grokking the System Design Interview course.

  1. How does one go about designing a traffic control system?

This is a classic system design interview question from the past that is still prevalent today. Make sure you understand how to transition from one state to another, such as RED to GREEN and GREEN to ORANGE to RED, and so on.

  1. How can you create a website similar to Pastebin?

Pastebin enables you to copy and paste text or code, then share a link to that code anywhere you choose. It is not an online code editor, but it may be used to store any kind of text.

  1. How would you go about creating your own Instagram?

Instagram is a popular photo- and video-sharing application that offers some unique filters to improve the quality of your photos. Your software should provide picture uploading, tagging images for search, and some basic filters. It would be fantastic if you can incorporate social media sharing, or social networking options themselves.

  1. How do you create a worldwide video streaming business similar to YouTube or Netflix?

How do you handle the difficulties of creating a video streaming service like Netflix or YouTube that requires seamless streaming, buffering, and operation over a low bandwidth connection? You can learn how to cope with such issues by taking a system design course.

Facebook System Design Interview Questions

Here are some commonly asked system design interview questions at Facebook:

  1. Design Facebook News Feed
  2. Design Facebook Status Search
  3. Design Facebook Messenger or WhatsApp
  4. Design Live Commenting
  5. Design Instagram
  6. Design Proximity Server
  7. Design Typeahead Suggestions
  8. Design Privacy Settings at Facebook
  9. Design Top N Songs
  10. Design Web Crawler

Other frequently asked system design interview questions include topics on concurrency (threads, deadlock, starvation, consistency, coherence), caching, database partitioning, replication, sharding, CAP theorem, networking (IPC, TCP/IP), real-world performance (relative performance RAM, disk, your network, SSD), availability and reliability (types of failures, failure units, how failures may manifest, mitigations, etc.), data storage and data aggregation, QPS capacity or machine estimation (back-of-the-envelope estimates), and byte size estimation.

Amazon System Design Interview Questions

To get you started, here are a few Amazon system design interview questions.

  1. How would you build a warehouse system for
  2. How would you build such that it could manage ten times as much traffic as it does now?
  3. How would you build the database for (customers, orders, goods, etc.)?
  4. Create an online service counters system.
  5. Create a chess game.
  6. Create a parking garage.
  7. Create an email sender with a capacity of 100,000,000 emails. You have five machines at your disposal. How would you go about doing it efficiently?
  8. Create a URL shortening service.
  9. Create a video-streaming service.
  10. Create an online bookshop.
  11. Create worldwide file storage or sharing service.
  12. Create an API rate limiter.
  13. Create a proximity server.
  14. Create a type-ahead service.
  15. How do you create a vending machine in Java?
  16. How does one go about designing a traffic control system?
  17. What is the best way to create a limit order book for trading systems?
  18. How does one go about designing an elevator system?
  19. How would you approach creating an e-commerce website?
  20. How would you approach building an e-commerce website using microservices? How will you manage business transactions?
  21. Create an autocomplete function similar to search engine word recommendations. How are you going to grow it to millions of users?

Interview Tips

  1. Begin simple and progress to the complexity

Because there isn’t enough time to study everything in detail, you need to be selective about it and focus on areas where you excel. Begin with breadth. Get a complete functioning solution, preferably with high-level components. You may then begin delving into the specifics of some of these components.

  1. Describe your thought process

The interviewer may direct you to topics that are important to them (or are more conducive to design conversations). Making arbitrary decisions without explaining them is unprofessional. Remember, you’re in charge of the interview. So don’t anticipate the interviewer to question you about everything you’re supposed to talk about to pass the interview. 

  1. Listen to the interviewer 

Although you are supposed to drive the interview, you must still listen. There are many areas to investigate in these issues, and the interviewer may be interested in a specific element. Pay attention to signals and go with the flow. Dismissing or avoiding a straight inquiry or request is a certain way to fail.

  1. Be confident

You are not expected to be an expert in everything. So, be confident but not arrogant. There will be certain elements of the system with which you will be unfamiliar. It’s much better to point them out than to make a mistake. Continue to try partial responses; these are typically sufficient.

You can also go for courses like Grokking The Design Interview, system design certification, and system design courses available out there to ensure you are ahead of the competition.

Frequently Asked Questions

How do I prepare for a system design interview?

To prepare for a system design interview, you should first organize your portfolio and prepare your resume and have copies on hand. Make sure you’ve researched the company and are looking your best. Arrive for the interview on time. You should also be prepared for other inquiries from the interviewer and have a list of questions to ask them as well.

Do you code in a system design interview?

System design interviews are more important for senior and higher-level jobs, while coding data structures, algorithms, and problem-solving interviews are common at all levels.

How do I prepare for the system design round?

Begin with high-level components and work your way down to detailed design. Start with covering the end-to-end process based on your objective and identifying the components needed to address the real problem or build your whole system.

Is system design hard?

Yes. System design is one of the most difficult subjects to master. Many applicants fail to answer questions on system architecture, scalability, load balancing, and failover, all of which are required to pass the interview.

Is system design easy?

If you are a complete beginner, the learning system design will typically take two months. But you will need to put in some effort to learn it. For all experienced applicants, knowing system design is a requisite for preparing for interviews.

Is system design a skill?

For experienced developers, system design is a distinguishing talent. The ability to program an algorithm or a data structure to address a specific issue is not the same as creating an end-to-end system. You need to be a competent system designer with a unique set of abilities.

Key Takeaways

The interview for system design is nothing more than a brainstorming session. Typically, these interviews begin with a high-level concept and subsequently descend to smaller components. Before going in for the interview, always conduct thorough research. Before answering any questions, try to listen attentively. Ensure that you’ve adequately prepared to confront a wide range of inquiries.

Instead of going into depth about one element, try to cover all of them briefly. Best wishes to all aspiring software engineers, developers, programmers, and designers!

Learn from the proven hacks on Coding Ninjas to crack high-level system design interviews. CodeStudio is a boot camp program that lets you practice and competes in challenges to prepare for tech interviews.