CodeSubmit Interview Series

The 8 Best System Design Interview Questions in 2023

Looking for the top system design interview questions? That’s what you’ll get here below. Read on!

Interviewing system designers

System design involves designing the architecture, components, and interactions of complex systems, as well as analyzing requirements, specifying system characteristics, creating models, and defining the overall behavior of the system. 

A system designer plays a crucial role in this process by collaborating with stakeholders to understand their needs and translating them into well-designed solutions. They look at things like scalability, reliability, performance, security, and usability. Some of the programming languages system designers are often familiar with include C++, Java, and Python.

But what are the top design interview questions to find system designers? Let’s take a look. 

Beginner system designer interview questions

Let’s start with the top interview questions for junior system designers.

1. You are tasked with designing a distributed file system that can handle large-scale data storage and retrieval. How would you approach this task, and what key components or concepts would you consider in your design?


When designing a distributed file system for large-scale data storage and retrieval, the following key components and concepts should be considered:

  1. Scalability: Distribute data across multiple servers for horizontal scaling and increased storage capacity.

  2. Fault tolerance: Replicate data to ensure system availability even if a server fails.

  3. Consistency and synchronization: Use distributed locks, transactions, or consensus protocols to maintain data consistency during concurrent operations.

  4. Metadata management: Store metadata separately and utilize distributed hash tables or databases for efficient management.

  5. Caching and data locality: Implement caching mechanisms to reduce disk accesses and improve performance.

  6. Security: Incorporate access controls, encryption, and authentication for data protection.

  7. Monitoring and logging: Build monitoring and logging capabilities for performance analysis and issue identification.

These components provide a foundation for designing an effective distributed file system, considering scalability, fault tolerance, consistency, metadata management, caching, security, and monitoring/logging.

2. Can you explain the principle of 'Separation of Concerns' and provide an example of how you have applied it in a past project?


'Separation of Concerns' is a design principle in software engineering where a system is broken down into distinct sections, each handling a specific aspect of the functionality. This approach leads to modular and easier-to-manage code.

In a recent project, I designed an online booking system. The system was split into three main components: User Interface (UI), Business Logic, and Data Storage. The UI was responsible for user interactions and input validation. The Business Logic handled processes like checking room availability and calculating charges. Finally, the Data Storage managed all data persistence and retrieval tasks.

By separating these concerns, we could change one component without affecting the others. For example, switching from a local database to a cloud-based one only involved updating the Data Storage component. The UI and Business Logic remained unaffected, making the transition seamless. This example emphasizes the power of 'Separation of Concerns' in maintaining and extending software systems.

3. Can you explain what 'scalability' means in the context of system design and provide an example of a design choice you made to improve system scalability?


'Scalability' refers to a system's ability to handle increased load — whether that's more users, more transactions, or more data — and to increase its capacity to maintain performance.

In a project where we built an eCommerce platform, I had to consider scalability due to the potential for high traffic during sale periods. To manage this, we implemented a load balancer to distribute incoming traffic evenly across multiple servers. This design choice allowed the system to handle a much larger number of simultaneous users without performance degradation.

Additionally, we used a NoSQL database for catalog data as it can handle large volumes of read operations quickly and scales out horizontally by adding more servers. These design choices improved the system's ability to scale up during peak periods and scale down during quieter times, optimizing resource usage and maintaining performance.

4. What is a RESTful API and how have you utilized one in a previous project?"


RESTful API stands for Representational State Transfer. It is a set of rules or conventions for building web services. It uses HTTP methods like GET, POST, PUT, DELETE for operations and can deliver data in various formats, but JSON is the most common.

In one of my previous projects, we developed a mobile application that needed to communicate with our server to fetch and update data. We designed a RESTful API on the server-side for this. This API provided endpoints corresponding to various resources like users, orders, and products.

For instance, we had a GET endpoint at '/users/{id}' to fetch details of a user, a POST endpoint at '/orders' to create a new order, and a PUT endpoint at '/products/{id}' to update a product's details. The mobile application could make HTTP requests to these endpoints to perform the required operations. This design provided a simple, stateless, and standardized way for our mobile application to communicate with the server.

Advanced system designer interview questions

Here are the top interview questions to ask senior system designers. 

5. Could you describe an experience where you implemented a high-availability system? What strategies did you employ to ensure system uptime?


Implementing high availability was crucial while building a payment processing system for an e-commerce platform. We adopted a microservices architecture, allowing each service to scale and fail independently, reducing the impact of any single failure.

We used master-slave replication in our database system to ensure data redundancy. If the master database failed, a slave could take over without data loss. We also utilized a distributed cache to lower the database load and provide quicker responses.

Finally, we incorporated load balancing and auto-scaling to handle traffic. Load balancers distributed traffic evenly, while auto-scaling adjusted server capacity based on load, ensuring we could handle peak traffic.

By combining these strategies, and conducting regular failover drills and performance tests, we achieved 99.99% system uptime.

6. Can you describe a time when you had to choose a particular database technology for a project? What factors did you consider in making this choice?


Choosing the correct database technology is pivotal for a project's success. In a previous role, we developed a real-time analytics platform that demanded fast read and write operations on large data volumes, making traditional relational databases unsuitable.

Considering the need for rapid data processing and scalability, we decided on a NoSQL database. The nature of our unstructured data and the requirement for horizontal scalability led us to choose Apache Cassandra, which is a database designed for handling vast amounts of data across many servers, providing high availability without a single point of failure.

Cassandra gave us the speed needed for read/write operations, the ability to store unstructured data, and the scalability to manage large data volumes. This choice was crucial for the project's successful execution.

7. How do you approach making decisions on integrating third-party services or APIs into a system? Can you give an example of a system where you made such decisions?


Deciding to integrate third-party services or APIs depends on factors like business needs, cost, development time, and the service's reliability and security.

While developing a social networking platform, we had a requirement for mapping and location services. Given the complexity of building such a feature and the robust solutions available, it made sense to use a third-party API.

We chose the Google Maps API after comparing several services, considering factors like cost, reliability, ease of integration, and data privacy policies. Google Maps provided accurate location data, was cost-effective, and its well-documented SDK eased integration.

Regular monitoring of the API's performance was also crucial to promptly address any issues, ensuring efficient resource use and adding significant value to our platform.

8. Can you describe a time when you had to refactor a complex system for improved performance and maintainability? What was your approach, and what outcomes did you achieve?


Refactoring a legacy e-commerce platform was one of the most impactful projects I've undertaken. This system had become complex and hard to maintain due to continual patches and additions.

We started by understanding the current system and identifying bottlenecks using code analysis and performance profiling tools. Prioritizing the areas that would yield the most value when refactored, we focused on database queries and data structures with significant performance impact.

We restructured these parts with modern design patterns and coding best practices, making them efficient and clear. We ensured the success of our refactoring by employing thorough unit, integration, and performance testing.

Post-refactoring, we saw faster response times and reduced server resource usage, indicating higher efficiency. The codebase became easier to maintain and enhance, leading to quicker feature development and bug resolution. This project underscored the value of regular refactoring in maintaining system performance and maintainability.

Over to you!

Now you know what the best system design interview questions are. 

However, interviews are just the first step. 

The next is to assess candidates. How? CodeSubmit helps you create coding assessment tests to evaluate your candidates before hiring them. 

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