Last Updated on May 25th, 2025

System design interviews have become a critical component of the technical hiring process at top tech companies, especially for mid-level to senior software engineering roles. Unlike coding interviews that focus on algorithms and data structures, system design interviews evaluate a candidate’s ability to architect scalable, efficient, and maintainable software systems.

In today’s world, where applications must support millions of users, handle large volumes of data, and provide high availability, companies look for engineers who understand distributed systems, microservices architecture, database sharding, caching, message queues, and more. These interviews help assess whether candidates can balance trade-offs between scalability, reliability, performance, and cost.

If you want to refresh concepts of System Design first, kindly visit a separate article on System Design Concepts.

In this article, we will explore System Design Interview Questions & Practice Test.

What Makes System Design Interviews Challenging?

A 2023 LinkedIn report revealed that 75% of candidates for senior engineering roles fail system design rounds due to gaps in addressing trade-offs (e.g., consistency vs. availability) or overlooking edge cases like latency spikes and database bottlenecks. Whether you’re designing a URL shortener, a parking lot system, or a real-time chat application, interviewers probe your capacity to balance theory (CAP theorem, sharding) with practicality (APIs, caching layers).

This shift reflects the industry’s demand for engineers who don’t just write code but solve infrastructure-scale problems. With companies increasingly prioritizing distributed systems expertise, mastering system design is not optional. It’s the #1 differentiator between a good candidate and a great one. Below are some facts that makes system design interviews challenging:

• Open-ended format: There is often no single “correct” solution.

• Breadth of knowledge: Requires understanding of multiple technologies and patterns.

• Communication skills: Candidates must clearly explain their design decisions.

• Real-world thinking: Reflects practical engineering skills used in the job.

This guide presents a comprehensive set of system design interview questions MCQs with detailed answers and explanations to help you boost your interview confidence.

System Design Interview Questions & Practice MCQs

Q#1: Functional Requirements in System Design (Multi-select)

A university is developing an e-learning platform and is documenting functional requirements. Which of the following would be classified as functional requirements for this system? (Select all that apply)

A) The system must allow instructors to upload course materials in various formats
B) The system must support at least 10,000 concurrent users
C) Students must be able to submit assignments and receive grades
D) The platform must be accessible to users with disabilities

Answer: A, C

Explanation:

• A) CORRECT. “The system must allow instructors to upload course materials in various formats” is a functional requirement as it describes a specific function or capability that the system must provide.
• B) INCORRECT. “The system must support at least 10,000 concurrent users” is a non-functional requirement related to performance and scalability. It describes how many users the system should handle, not what functionality it provides.
• C) CORRECT. “Students must be able to submit assignments and receive grades” is a functional requirement as it describes specific features or capabilities that the system must provide to users.
• D) INCORRECT. “The platform must be accessible to users with disabilities” is a non-functional requirement related to accessibility. It describes a quality attribute of the system rather than a specific function.

Q#2. Horizontal vs Vertical Scaling (Single-select)

An e-commerce platform experiences performance degradation during flash sales when product page views increase by 500%. The development team has determined that the database is the bottleneck. Which scaling approach would be MOST appropriate to address this specific issue?

A) Horizontal scaling by adding more web servers
B) Vertical scaling by upgrading the database server's CPU and memory
C) Horizontal scaling by implementing database sharding
D) Vertical scaling by optimizing the web server code

Answer: C

Explanation:

• A) INCORRECT. Adding more web servers (horizontal scaling) would help with web traffic processing but wouldn’t address the database bottleneck, which is the identified issue.
• B) INCORRECT. While upgrading the database server’s resources (vertical scaling) might provide some relief, it has physical limitations and may not be sufficient for a 500% increase in traffic. Additionally, vertical scaling often requires downtime for upgrades.
• C) CORRECT. Database sharding (horizontal scaling) distributes the database load across multiple servers by partitioning the data. This approach is most appropriate for handling the 500% increase in database load during flash sales because it provides better scalability than vertical scaling and directly addresses the database bottleneck.
• D) INCORRECT. Optimizing web server code is not a scaling approach and wouldn’t address the database bottleneck, which is the identified issue.

Q#3: Saga Pattern (Multi-select)

Which of the following are characteristics of the Saga pattern in distributed transactions? (Select all that apply)

A) It maintains ACID properties across all services
B) It implements a sequence of local transactions with compensating transactions
C) It requires a central coordinator to manage the entire transaction
D) It provides eventual consistency rather than strong consistency

Answer: B, D

Explanation:

• A) INCORRECT. The Saga pattern does not maintain ACID properties across services; it’s specifically designed to handle scenarios where ACID transactions aren’t feasible.
• B) CORRECT. Sagas implement a sequence of local transactions, each with a compensating transaction that can undo its effects if a later step fails.
• C) INCORRECT. While some saga implementations use orchestration with a central coordinator, choreography-based sagas don’t require a central coordinator.
• D) CORRECT. Sagas provide eventual consistency rather than strong consistency, as there may be intermediate states where the system is inconsistent.

Q#4: Monolithic vs Microservices Architecture (Single-select)

Which statement accurately describes a key architectural difference between monolithic and microservices architectures?

A) Monolithic architectures typically have higher deployment frequency than microservices
B) Microservices architectures typically use a single shared database for data consistency
C) Monolithic architectures package all functionality in a single deployable unit
D) Microservices architectures require all services to be written in the same programming language

Answer: C

Explanation:

• A) INCORRECT. Microservices typically enable higher deployment frequency as individual services can be deployed independently.
• B) INCORRECT. Microservices typically use separate databases per service (database per service pattern), not a single shared database.
• C) CORRECT. In a monolithic architecture, all functionality is packaged and deployed as a single unit, making it more difficult to scale or modify individual components independently.
• D) INCORRECT. One advantage of microservices is polyglot programming, allowing different services to use different programming languages based on their specific requirements.

Q#5. Service Discovery (Multi-select)

Which of the following are valid approaches for service discovery in a microservices architecture? (Select all that apply)

A) Client-side discovery with a service registry
B) Server-side discovery with a load balancer
C) DNS-based discovery
D) Hard-coded service URLs in application configuration

Answer: A, B, C

Explanation:

• A) CORRECT. Client-side discovery involves clients querying a service registry to find available service instances and then making requests directly to them.
• B) CORRECT. Server-side discovery involves clients making requests through a load balancer that queries the service registry and forwards requests to available instances.
• C) CORRECT. DNS-based discovery uses DNS SRV records or similar mechanisms to locate services, which can be effective especially with systems that support DNS-based routing.
• D) INCORRECT. Hard-coded service URLs are not a proper service discovery mechanism as they don’t adapt to dynamic environments where service instances may change.

Q#6. Monolithic vs Microservices (Single-select)

A startup is developing a new project management application and is deciding between a monolithic or microservices architecture. The company has a small development team of five engineers, expects moderate user growth in the first year, and needs to launch quickly. Which architecture would be MOST appropriate for their situation?

A) Microservices architecture with services for each project management function
B) Monolithic architecture with well-defined internal modules
C) Hybrid architecture with core features as microservices and supporting features as monoliths
D) Serverless architecture with function-as-a-service components

Answer: B

Explanation:

• A) INCORRECT. A microservices architecture would introduce unnecessary complexity for a small team and initial product. The operational overhead of managing multiple services would slow down the development and launch process.
• B) CORRECT. A monolithic architecture with well-defined internal modules is most appropriate for this scenario. With a small team, limited initial scale requirements, and the need for rapid development, a monolith offers simplicity in development, deployment, and operations. Well-defined internal modules maintain good code organization while avoiding the operational complexity of microservices.
• C) INCORRECT. A hybrid architecture adds complexity without clear benefits in this scenario. For a small team with moderate growth expectations, managing even some microservices would introduce overhead that isn’t justified by the requirements.
• D) INCORRECT. While serverless architecture can reduce operational overhead, it introduces different complexities around state management, local development, and testing that might slow down the initial development process for a small team.

Q#7. Object-Oriented Analysis and Design (Single-select)

A team is designing a library management system using Object-Oriented Analysis and Design (OOAD). They have identified the following classes: Book, Member, Librarian, and Transaction. Which relationship would MOST accurately represent the association between Book and Transaction?

A) Inheritance, as Transaction is a type of Book
B) Composition, as Book contains Transactions
C) Association, as Transaction references Book
D) Dependency, as Book creates Transaction

Answer: C

Explanation:

• A) INCORRECT. Inheritance represents an “is-a” relationship, but a Transaction is not a type of Book. These are distinct entities with different purposes in the library system.
• B) INCORRECT. Composition represents a “contains” relationship where the contained object cannot exist without the container. Transactions don’t physically exist inside Books, and they can exist independently of any specific Book.
• C) CORRECT. Association represents a relationship where objects are connected but exist independently. In a library system, a Transaction would reference a Book (and likely a Member), but all entities exist independently. The Transaction needs to know which Book is being borrowed/returned, making this an association relationship.
• D) INCORRECT. Dependency implies that Book creates Transaction, which is not accurate in a library system. Typically, a Librarian or the system would create a Transaction when a Member borrows or returns a Book.

Q#8. Latency and Throughput (Single-select)

A video streaming service is experiencing user complaints about buffering during peak hours. The engineering team has collected the following metrics:

– Average request latency: 200ms

– Server CPU utilization: 45%

– Network bandwidth utilization: 85%

– Database query response time: 50ms

Based on these metrics, which component is MOST likely the bottleneck causing the buffering issues?

A) Application server processing
B) Database performance
C) Network bandwidth
D) Client-side rendering

Answer: C

Explanation:

• A) INCORRECT. With CPU utilization at only 45%, the application servers have sufficient capacity and are not likely to be the bottleneck.
• B) INCORRECT. Database query response time of 50ms is relatively low and unlikely to cause video buffering issues, especially since video content is typically not served directly from databases.
• C) CORRECT. Network bandwidth utilization at 85% is the most likely bottleneck. Video streaming is bandwidth-intensive, and high utilization (approaching 90%) can lead to network congestion, packet loss, and inconsistent delivery rates—all of which cause buffering. This is especially problematic during peak hours when many users are streaming simultaneously.
• D) INCORRECT. Client-side rendering issues would typically manifest differently across various devices and wouldn’t be directly related to peak hour usage. The symptoms described point to a server or network issue rather than client-side problems.

Q#9. Microservices Communication Patterns (Multi-select)

A retail company is implementing a microservices architecture for their order processing system. Which communication patterns would be appropriate for different aspects of this system? (Select all that apply)

A) Synchronous REST calls for real-time inventory checks during checkout
B) Asynchronous messaging for order fulfillment and shipping notifications
C) Shared database for order and customer information across all services
D) Event sourcing for tracking the complete history of order status changes

Answer: A, B, D

Explanation:

• A) CORRECT. Synchronous REST calls are appropriate for real-time inventory checks during checkout because the customer needs immediate confirmation that the items are available before completing their purchase. This is a scenario where waiting for a response is necessary.
• B) CORRECT. Asynchronous messaging is appropriate for order fulfillment and shipping notifications because these processes happen after the order is placed and don’t require immediate customer interaction. Using message queues allows these processes to be handled independently and ensures messages aren’t lost even if a service is temporarily unavailable.
• C) INCORRECT. A shared database across all services violates the microservices principle of database independence. This approach creates tight coupling between services and makes independent scaling and deployment difficult.
• D) CORRECT. Event sourcing is appropriate for tracking the complete history of order status changes. By storing each state change as an immutable event, the system maintains a complete audit trail of an order’s lifecycle, which is valuable for troubleshooting issues and providing customer support.

Q#10. System Design for High Availability (Single-select)

In designing a system for high availability, which approach would provide the LEAST improvement to overall system uptime?

A) Increasing the complexity of each service to reduce the number of services
B) Deploying the application across multiple availability zones
C) Implementing redundant load balancers with automatic failover
D) Using a database with automatic primary-replica failover

Answer: A

Explanation:

• A) CORRECT. Increasing service complexity would provide the LEAST improvement to availability. Complex services are more prone to failures and harder to debug, potentially reducing availability rather than improving it.
• B) INCORRECT. Multi-AZ deployment protects against datacenter-level failures, significantly improving availability.
• C) INCORRECT. Redundant load balancers with automatic failover eliminate a single point of failure and improve availability.
• D) INCORRECT. Database failover capabilities ensure database availability even if the primary instance fails.

Q#11. CQRS Pattern (Multi-select)

Which of the following are valid benefits of implementing the Command Query Responsibility Segregation (CQRS) pattern? (Select all that apply)

A) Simplified data models by using a single model for both reads and writes
B) Optimized read and write operations with different data models
C) Independent scaling of read and write workloads
D) Reduced system complexity through unified processing paths

Answer: B, C

Explanation:

• A) INCORRECT. CQRS actually separates read and write models rather than using a single model.
• B) CORRECT. CQRS allows optimization of read and write operations independently with different data models tailored to their specific needs.
• C) CORRECT. With separate read and write services, CQRS enables independent scaling based on the different workload characteristics of each.
• D) INCORRECT. CQRS typically increases system complexity by introducing separate processing paths, though this complexity is a trade-off for other benefits.

Q#12. API Design Styles (Multi-select)

Which of the following are recognized API architectural styles? (Select all that apply)

A) REST (Representational State Transfer)
B) GraphQL
C) MQTT (Message Queuing Telemetry Transport)
D) MVC (Model-View-Controller)

Answer: A, B, C

Explanation:

• A) CORRECT. REST is a widely used architectural style for designing networked applications, particularly web APIs.
• B) CORRECT. GraphQL is an API query language and runtime for fulfilling those queries, providing an alternative to REST.
• C) CORRECT. MQTT is a lightweight messaging protocol designed for constrained devices and low-bandwidth, high-latency networks, commonly used in IoT applications.
• D) INCORRECT. MVC is a software design pattern for implementing user interfaces, not an API architectural style.

Q#13. Database Normalization (Single-select)

In system design, when might denormalization of a database schema be appropriate?

A) When data integrity is the highest priority
B) When read performance is critical and data is read much more frequently than it is updated
C) When the system needs to support complex tansactions across multiple entities
D) When storage space optimization is the primary concern

Answer: B

Explanation:

• A) INCORRECT. Normalization, not denormalization, prioritizes data integrity by reducing redundancy.
• B) CORRECT. Denormalization is appropriate when read performance is critical and data is read much more frequently than updated, as it can reduce the need for joins and improve read performance at the cost of some data redundancy.
• C) INCORRECT. Normalized schemas are generally better for complex transactions across multiple entities.
• D) INCORRECT. Normalization, not denormalization, typically optimizes storage space by reducing redundancy.

Q#14. Microservices Security (Single-select)

Which security pattern involves verifying the identity of both the client and the server during TLS handshake?

A) Basic Authentication
B) OAuth 2.0
C) Mutual TLS (mTLS)
D) API Keys

Answer: C

Explanation:

• A) INCORRECT. Basic Authentication only verifies the client’s identity, not the server’s.
• B) INCORRECT. OAuth 2.0 is an authorization framework, not specifically about mutual authentication during TLS handshake.
• C) CORRECT.Mutual TLS (mTLS) involves verifying the identity of both the client and the server during TLS handshake, using certificates on both sides.
• D) INCORRECT. API Keys only verify the client’s identity, not the server’s.

Q#15. Low-Level Design Components (Single-select)

A team is developing a customer relationship management (CRM) system and has completed the high-level design. Which artifact would be MOST appropriate to include in the low-level design documentation?

A) System context diagram showing external interfaces
B) Detailed class diagrams with attributes and methods
C) Business requirements document
D) High-level component interaction diagram

Answer: B

Explanation:

• A) INCORRECT. A system context diagram showing external interfaces is typically part of high-level design documentation, not low-level design. It provides a broad overview of system boundaries rather than implementation details.
• B) CORRECT. Detailed class diagrams with attributes and methods are a core component of low-level design documentation. These diagrams specify the internal structure of the system at the implementation level, showing classes, their attributes, methods, and relationships. This level of detail is precisely what distinguishes low-level design from high-level design.
• C) INCORRECT. The business requirements document is created during the requirements gathering phase, well before low-level design. It describes what the system should do, not how it should be implemented.
• D) INCORRECT. A high-level component interaction diagram belongs in the high-level design documentation. It shows major components and their interactions but lacks the implementation details required for low-level design.

Q#16. System Design Life Cycle (Single-select)

A government agency is developing a critical infrastructure monitoring system with strict regulatory compliance requirements. During which phase of the System Design Life Cycle (SDLC) should compliance verification be PRIMARILY conducted?

A) Requirements Analysis
B) Design
C) Implementation
D) Testing and Validation

Answer: D

Explanation:

• A) INCORRECT. Requirements Analysis is where compliance requirements are identified and documented, but not where they are verified. This phase focuses on understanding what needs to be built, including compliance requirements.
• B) INCORRECT. Design phase incorporates compliance considerations into the system architecture, but doesn’t verify that the implemented system actually meets these requirements.
• C) INCORRECT. Implementation is where the system is built according to design specifications, including compliance features, but verification happens after implementation.
• D) CORRECT. Testing and Validation is the primary phase for compliance verification. This is where the implemented system is thoroughly tested against all requirements, including regulatory compliance. For a critical infrastructure system with strict regulatory requirements, comprehensive validation testing is essential to ensure all compliance aspects are properly implemented before deployment.

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You may also want to go through a real world example: Java System Design- Hospital Management System