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How to Crack System Design Interview Round?

Last Updated : 02 Jan, 2025
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In the System Design Interview round, You will have to give a clear explanation about designing large scalable distributed systems to the interviewer. This round may be challenging and complex for you because you are supposed to cover all the topics and tradeoffs within this limited time frame, which seems impossible. But this article will work as a guide to solve all these doubts and problems and make you excel in the System Design Interview Round.

How-to-Crack-System-Design-Round-in-Interviews

Table of Content

Steps to Crack System Design Round in Interviews

We know that it might be an difficult round for you so let's start discussing step-by-step approach and try to make this round easier for you.

Apart from that, if you want to crack the interview rounds smoothly then enroll now with GeeksforGeeks Mastering System DesignCourse, mentored by experts. 

Step 1. Understand the Goal and Gather All the Requirements

System design interview questions, by nature, are unclear or abstract. Asking questions about the exact scope of the problem, and clarifying functional requirements early in the interview is essential. Usually, requirements are divided into three parts:

How-to-crack-System-design-round-1

1.1 Functional Requirements

These are the requirements that the end user specifically demands as basic functionalities that the system should offer. All these functionalities need to be necessarily included into the system as part of the contract.

For example:

  • "What are the features that we need to design for this system?"
  • "What are the edge cases we need to consider, if any, in our design?"

1.2 Non-Functional Requirements

These are the quality constraints that the system must satisfy according to the project contract. The priority or extent to which these factors are implemented varies from one project to another. They are also called non-behavioral requirements. For example, portability, maintainability, reliability, scalability, security, etc.

For example:

  • "Each request should be processed with the minimum latency"
  • "System should be highly available"

1.3 Extended requirements

These are basically "nice to have" requirements that might be out of the scope of the system.

For example:

  • "Our system should record metrics and analytics"
  • "Service health and performance monitoring?"

Step 2. Understand the Estimation and Constraints

Estimate the scale of the system we're going to design. focus on the system’s expected scale (like user volume and request rates) and practical limits (like latency and budget). This helps guide your design choices, ensuring the solution can handle expected demand. It is important to ask questions such as:

  • "What is the desired scale that this system will need to handle?"
  • "What is the read/write ratio of our system?"
  • "How many requests per second?"
  • "How much storage will be needed?"

These questions will help us scale our design later.

Step 3. High-level component design

Now it's time to identify system components (such as Load Balancers, API Gateway, etc.) that are needed to solve our problem and draft the first design of our system and outline the flow of data between them. This gives an organized view of the system’s architecture and sets up a foundation for further detailed design.

Once we have a basic diagram, we can start discussing with the interviewer how the system will work from the client's perspective.

Step 4. Detailed design or Low-Level Design(LLD)

Now it's time to go into detail about the major components of the system we designed. As always discuss with the interviewer which component may need further improvements.

Here is a good opportunity to demonstrate your experience in the areas of your expertise. Present different approaches, advantages, and disadvantages. Explain your design decisions, and back them up with examples. This is also a good time to discuss any additional features the system might be able to support, though this is optional.

  • "How should we partition our data?"
  • "What about load distribution?"
  • "Should we use cache?"
  • "How will we handle a sudden spike in traffic?"

Also, try not to be biased about certain technologies, statements like "I believe that NoSQL databases are just better, SQL databases are not scalable" reflect the candidate's understanding very poorly.

Step 5. Define the Data model design

How-to-crack-System-design-round-3

Now we can start with defining the database schema. Doing so would help us to understand the data flow which is the core of every system. In this step, we basically define all the entities and relationships between them.

  • "What are the different entities in the system?"
  • "What are the relationships between these entities?"
  • "How many tables do we need?"
  • "Is NoSQL a better choice here?"

Step 6. API design

How-to-crack-System-design-round-2

Next, we can start designing APIs for the system. These APIs will help us define the expectations from the system explicitly. We don't have to write any code, just a simple interface defining the API requirements such as parameters, functions, classes, types, entities, etc.

For example:

API 
createUser(name: string, email: string): User

It is advised to keep the interface as simple as possible and come back to it later when covering extended requirements.

Step 7. Identify and resolve bottlenecks

Now at this point you can discuss bottlenecks in the system and approaches to mitigate them. Here are some important questions to ask:

  • "Do we have enough database replicas?"
  • "Is there any single point of failure?"
  • "Is database sharding required?"
  • "How can we make our system more robust?"
  • "How to improve the availability of our cache?"

Make sure to read the engineering blog of the company you're interviewing with. This will help you get a sense of what technology stack they're using and which problems are important to them.

Most Frequently asked Problems for System Design

Below, are some question which is most frequently asked in system design for designing purpose:

1. Design URL Shortener like TinyURL

2. Design Youtube

3. Design Netflix

4. Design Facebook

5. Design Google Maps

6. Design Autocomplete for Search Engines

7. Design Uber

8. Design Spotify

9. Design Rate Limiter

10. Design Parking Garage

11. Design Vending Machine

Quick Tips and Strategies for Succeding in System Design Interview Round

Try to follow the 80-20 rule during your interview, where 80% of the time you will be speaking and explaining everything and 20% of the time your interviewer. Don't use buzzwords and don't pretend to be an expert if you don't know something.

  • You read read some blog posts or a few topics, if today and tomorrow is your interview, during your interview if you throw some buzzwords like "No-SQL", "Mongo DB" and "Cassandra" then it may backfire on you.
    • You can't make a fool of the interviewer who is an industry expert, always consider that your interviewer may ask for more details and justification so if you are using technology X or database Y then "why?", prepare yourself for this kind of question.
  • Do not go into detail prematurely.
    • Many times it happens when a candidate starts explaining one part of the system, they go into too much detail about the component and forget about the strict timeframe and other components.
    • Maybe the interviewer wants you to stop somewhere where they don't need too much detail. So to avoid this mistake wait for the interviewer's feedback or response.
  • Don't have a set architecture in mind
    • Like MVC or event-driven and try to fit the requirement somehow in that architecture. Maybe it's not suitable as per the requirement. Requirements may change during the interview to test your flexibility.
  • Be honest during your interviews
    • If you have never used technology X then you don't need to be fake in that situation. Try to find common solutions and show them your honesty, confidence, and willingness to learn something. That will make a good impression on the interviewer.

Do's and Dont's in System Design Interview Round

Let’s try to make it simple and discuss some key points before you start your preparation for this round.

  • Consider your interviewer as a team member and take this round as an opportunity to work with him where you both are supposed to solve a real-world problem related to your company's goal but here you need to take ownership and lead everything.
  • The main purpose of this round is to understand how capable you are of building a large-scale system and your thought process behind designing a service. Clarity of thoughts matters a lot because if you can explain it to the interviewer, you can do this in your team as well.
  • One of the good things for you in this round is that you are supposed to come up with the best solution for all kinds of open-ended problems instead of accurate solutions. Your ability to articulate your thoughts matters more than the final design you present to them.

System Design Interview Prepation Roadmap

1. System Design Fundamentals

2. Low-Level Design (LLD) Preparation

3. High-Level Design (HLD) Preparation

4. Interview Preparation Resources



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System Design Interview Questions and Answers [2025]

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