50 Advanced System Design Interview Questions to Prepare
Preparing for system design interviews can be challenging, especially when aiming for advanced or senior engineering roles.
To help you succeed, it's crucial to understand key system design concepts and tackle the most common system design interview questions.
This blog presents 50 advanced system design questions and concepts that are frequently asked in technical interviews. Each question is paired with a clear and simple answer, making your system design interview preparation more effective and less stressful.
Whether you're looking to master scalable systems, delve into system architecture, or grasp essential system design principles, this guide has you covered.
Let’s cover these questions to make your system design interview preparation smoother!
1. Scalability and Performance
1. What is horizontal scaling versus vertical scaling? Explain the benefits and drawbacks of each.
Horizontal scaling involves adding more machines to handle increased load, which improves fault tolerance and flexibility.
Vertical scaling means upgrading the existing machine's resources, like CPU or RAM. Horizontal scaling is more scalable long-term, while vertical scaling is simpler but limited by hardware constraints.
2. Define load balancing and describe different load balancing algorithms.
Load balancing distributes incoming network traffic across multiple servers to ensure no single server is overwhelmed. Common algorithms include Round Robin (distributes requests evenly), Least Connections (sends to the server with fewest active connections), and IP Hash (routes based on client IP).
3. Explain the CAP Theorem and its implications in distributed systems.
The CAP Theorem states that a distributed system can only guarantee two out of three properties:
Consistency (all nodes see the same data), Availability (every request gets a response), and Partition Tolerance (system continues despite network splits). Designers must choose which two to prioritize based on application needs.
4. What is latency, and how does it differ from throughput?
Latency is the time it takes for a single request to be processed, while throughput measures how many requests can be handled in a given time. Low latency ensures quick responses, and high throughput ensures the system can handle many requests efficiently.
5. Describe the concept of backpressure in system design.
Backpressure is a mechanism to prevent systems from being overwhelmed by controlling the flow of data. When a system component is slow, backpressure signals upstream components to slow down or pause sending data, ensuring stability and preventing crashes.
Section 2. Data Storage and Management
6. What are the differences between SQL and NoSQL databases? Provide use-case scenarios for each.
SQL databases are relational, use structured schemas, and are ideal for applications requiring complex queries and transactions, like banking systems.
NoSQL databases are non-relational, flexible with data models, and suited for large-scale data storage, such as social media platforms or real-time analytics.
7. Explain data sharding and its role in database scalability.
Data sharding splits a database into smaller, more manageable pieces called shards, each holding a subset of the data. This allows databases to scale horizontally by distributing shards across multiple servers, improving performance and handling larger volumes of data.
8. Define eventual consistency and strong consistency. When would you choose one over the other?
Strong consistency ensures that all users see the same data at the same time.
Eventual consistency means that all updates will propagate to all nodes eventually, but not instantly. Use strong consistency for critical data like financial transactions and eventual consistency for applications like social media feeds where slight delays are acceptable.
9. What is ACID compliance in databases? Explain each component.
ACID stands for Atomicity (transactions are all-or-nothing), Consistency (transactions bring the database from one valid state to another), Isolation (transactions do not interfere with each other), and Durability (once a transaction is committed, it remains so). These properties ensure reliable and predictable database operations.
10. Describe the concept of data partitioning and replication.
Data partitioning divides a database into distinct sections to improve performance and manageability.
Replication involves copying data across multiple servers to enhance availability and fault tolerance. Together, they help in scaling databases and ensuring data reliability.
Section 3. Reliability and Availability
11. What is high availability, and how is it achieved in system design?
High availability ensures that a system is operational and accessible almost all the time. It is achieved through redundancy (multiple servers), failover mechanisms, load balancing, and regular maintenance to minimize downtime.
12. Define fault tolerance and explain how it differs from high availability.
Fault tolerance is the ability of a system to continue operating properly even if some components fail. While high availability focuses on minimizing downtime, fault tolerance ensures the system remains functional despite failures by having backup components and error-handling mechanisms.
13. Explain the concept of redundancy and its importance in system reliability.
Redundancy involves having extra components or systems in place to take over if primary ones fail. It is crucial for reliability as it prevents single points of failure, ensuring the system remains operational even when parts of it experience issues.
14. What are failover strategies, and how do they contribute to system availability?
Failover strategies are methods to switch to a standby system when the primary system fails. Techniques include active-passive (standby activates upon failure) and active-active (both systems handle traffic and take over seamlessly). They enhance availability by ensuring continuous service during failures.
15. Describe the difference between active-active and active-passive architectures.
In active-active architectures, multiple systems handle requests simultaneously, providing load balancing and redundancy. In active-passive setups, one system is active while others remain on standby, taking over only if the active system fails. Active-active offers better load distribution, while active-passive is simpler to implement.
Section 4. Security and Compliance
16. What is OAuth 2.0, and how does it facilitate secure authorization?
OAuth 2.0 is an authorization framework that allows applications to obtain limited access to user accounts on an HTTP service. It enables secure delegated access by allowing users to grant access without sharing their credentials, enhancing security for APIs and services.
17. Explain the principle of least privilege in system security.
The principle of least privilege ensures that users and systems have only the minimum access necessary to perform their functions. This reduces the risk of unauthorized access or accidental misuse, enhancing overall system security.
18. Define encryption at rest and encryption in transit. Why are both important?
Encryption at rest protects data stored on disks, ensuring it remains secure if the storage medium is compromised.
Encryption in transit secures data as it moves between systems or over networks. Both are vital to protect data from unauthorized access and breaches at different stages.
19. What are common security vulnerabilities in web applications, and how can they be mitigated?
Common vulnerabilities include SQL injection, cross-site scripting (XSS), cross-site request forgery (CSRF), and broken authentication. Mitigation involves input validation, using prepared statements, implementing proper authentication mechanisms, and regularly updating and patching software.
20. Describe the role of a firewall in network security.
A firewall acts as a barrier between a trusted internal network and untrusted external networks. It monitors and controls incoming and outgoing traffic based on security rules, helping prevent unauthorized access and protecting against threats like malware and hackers.
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Section 5. Networking and Communication
21. What is a CDN (Content Delivery Network), and how does it improve system performance?
A CDN is a network of geographically distributed servers that deliver content to users from the nearest location. This reduces latency, speeds up content delivery, and decreases the load on the origin server, improving overall system performance and user experience.
22. Explain the difference between synchronous and asynchronous communication in microservices.
Synchronous communication requires the service making the request to wait for a response, leading to tighter coupling.
Asynchronous communication allows services to communicate without waiting for immediate responses, promoting loose coupling and better scalability.
23. Define API gateway and its functionalities in a microservices architecture.
An API gateway acts as a single entry point for all client requests in a microservices architecture. It handles tasks like routing, load balancing, authentication, rate limiting, and aggregating responses from multiple services, simplifying client interactions with the system.
24. What is gRPC, and how does it compare to REST?
gRPC is a high-performance, open-source framework for remote procedure calls using HTTP/2 and Protocol Buffers. Compared to REST, gRPC offers faster communication, better support for streaming, and a more efficient binary format, making it suitable for inter-service communication in microservices.
Learn more about REST vs. gRPC comparison.
25. Describe the concept of service discovery in distributed systems.
Service discovery allows services within a distributed system to find and communicate with each other dynamically. It typically involves a registry where services register themselves, and clients query the registry to locate service instances, enabling scalability and flexibility.
Section 6. Caching and Content Delivery
26. What is caching, and how does it enhance system performance?
Caching stores frequently accessed data in a faster storage layer, like memory, to reduce retrieval times. It enhances performance by minimizing the need to access slower databases or storage systems, leading to quicker responses and reduced load on backend resources.
27. Explain the differences between client-side caching and server-side caching.
Client-side caching stores data on the user's device, reducing the need to fetch data from the server repeatedly.
Server-side caching stores data on the server, allowing multiple clients to access cached data quickly. Both reduce latency and improve performance but operate at different points in the system.
28. Define cache eviction policies and describe common types.
Cache eviction policies determine which data to remove when the cache is full. Common types include Least Recently Used (LRU), which removes the least accessed items, First In First Out (FIFO), which removes the oldest items, and Least Frequently Used (LFU), which removes the least accessed items over time.
29. What is a cache miss, and how can it be minimized?
A cache miss occurs when the requested data is not found in the cache, requiring retrieval from the primary data source. It can be minimized by optimizing cache size, using effective eviction policies, preloading frequently accessed data, and ensuring data consistency between the cache and the source.
30. Describe the role of a CDN in caching static and dynamic content.
A CDN caches static content like images, videos, and stylesheets at edge servers close to users, reducing load times.
For dynamic content, CDNs can cache responses or use techniques like edge computing to process requests closer to the user, improving performance even for content that changes frequently.
Section 7. Search and Recommendation Systems
31. What is indexing in search engines, and why is it important?
Indexing involves organizing data in a way that allows for fast retrieval during searches. It is important because it significantly speeds up query responses by enabling the search engine to quickly locate relevant information without scanning the entire dataset.
32. Explain the concept of inverted indexes and their use in search systems.
An inverted index maps content, like words or terms, to their locations within a set of documents. It is used in search systems to quickly find all documents containing a specific term, making search operations much faster and more efficient.
33. Define relevance ranking and its significance in search results.
Relevance ranking determines the order in which search results are presented based on how well they match the query. It is significant because it ensures users see the most pertinent and useful results first, enhancing the search experience and satisfaction.
34. What are collaborative filtering and content-based filtering in recommendation systems?
Collaborative filtering makes recommendations based on user behavior and preferences by finding similarities between users or items.
Content-based filtering recommends items similar to those a user has liked in the past by analyzing item features. Both methods help personalize user experiences.
35. Describe the cold start problem in recommendation systems and potential solutions.
The cold start problem occurs when a system lacks sufficient data about new users or items to make accurate recommendations. Solutions include using default recommendations, leveraging content-based filtering, incorporating demographic information, and encouraging user interactions to gather initial data.
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Section 8. Real-Time Processing and Event Handling
36. What is stream processing, and how does it differ from batch processing?
Stream processing handles data in real-time as it arrives, allowing immediate analysis and action.
Batch processing collects data over a period and processes it all at once. Stream processing is ideal for applications requiring instant insights, while batch is suitable for periodic analysis.
37. Explain the concept of event sourcing in system design.
Event sourcing records all changes to the application's state as a sequence of events. Instead of storing the current state, the system reconstructs it by replaying events. This approach provides a complete history, enabling features like audit trails and easier debugging.
38. Define the role of a message broker in event-driven architectures.
A message broker facilitates communication between different parts of a system by receiving, storing, and forwarding messages. It decouples producers and consumers, enabling scalable and reliable event-driven architectures where components can operate independently.
39. What is windowing in real-time data processing?
Windowing divides continuous data streams into manageable chunks or "windows" based on time or count. This allows systems to perform computations and analysis on specific segments of the data stream, making real-time processing more efficient and organized.
40. Describe the concept of exactly-once processing semantics.
Exactly-once processing ensures that each message or event is processed only once, avoiding duplicates. This is crucial for maintaining data accuracy and consistency, especially in systems where duplicate processing can lead to errors or incorrect results.
Section 9. APIs and Integration
41. What is RESTful API design, and what are its key principles?
RESTful API design follows the principles of Representational State Transfer (REST). Key principles include using standard HTTP methods (GET, POST, PUT, DELETE), stateless communication, resource-based URLs, and leveraging HTTP status codes for responses, ensuring scalability and simplicity.
42. Explain the differences between REST and GraphQL APIs.
REST APIs use fixed endpoints and return predefined data structures, which can lead to over-fetching or under-fetching data.
GraphQL allows clients to request exactly the data they need through flexible queries, reducing data transfer and improving efficiency for complex applications.
43. Define API versioning and its importance in maintaining backward compatibility.
API versioning involves creating different versions of an API to introduce changes without disrupting existing clients. It is important for maintaining backward compatibility, allowing developers to update and improve APIs while ensuring that older applications continue to function correctly.
Learn about the 18 System Design concepts essential for engineers.
44. What are webhooks, and how are they used in system integrations?
Webhooks are HTTP callbacks that notify external systems about events in real-time. They are used in integrations to allow one application to send data to another automatically when specific events occur, enabling seamless and timely interactions between different services.
45. Describe the concept of API throttling and rate limiting.
API throttling and rate limiting control the number of requests a client can make to an API within a specific time frame. This prevents abuse, ensures fair usage, protects the system from overload, and maintains performance by regulating traffic.
Section 10. Advanced Topics
46. What is microservices architecture, and how does it compare to monolithic architecture
Microservices architecture breaks an application into small, independent services that communicate over APIs. Compared to monolithic architecture, where all components are tightly integrated, microservices offer better scalability, flexibility, and easier maintenance but require more complex management and coordination.
Check out more about the microservices vs. monolithic architecture.
47. Explain the concept of containerization and its benefits in system deployment.
Containerization packages applications and their dependencies into lightweight, portable containers. Benefits include consistency across environments, easier scaling, faster deployment, and improved resource utilization, making it easier to develop, test, and deploy applications.
48. Define serverless architecture and discuss its advantages and limitations.
Serverless architecture allows developers to build and run applications without managing servers. Advantages include reduced operational overhead, automatic scaling, and cost efficiency based on usage. Limitations include potential vendor lock-in, limited control over the infrastructure, and challenges with cold starts and debugging.
49. What is a distributed ledger, and how does it relate to blockchain technology?
A distributed ledger is a database that is consensually shared and synchronized across multiple locations.
Blockchain is a type of distributed ledger that records transactions in a secure, immutable chain of blocks, enabling decentralized and transparent systems like cryptocurrencies.
50. Describe the role of orchestration tools like Kubernetes in managing microservice.
Orchestration tools like Kubernetes automate the deployment, scaling, and management of microservices. They handle tasks such as container scheduling, load balancing, service discovery, and ensuring high availability, making it easier to manage complex, distributed applications.
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Final Thoughts
Mastering advanced system design concepts takes time and practice, but having the right questions and answers can make all the difference.
The 50 questions we covered provide a solid foundation to help you understand the essential principles and prepare for the challenges of technical interviews.
Remember to review these concepts, think about how they apply to real-world scenarios, and practice explaining them clearly.
Good luck!
