10 Must-Do System Design Interview Questions (with Answers)

Question 1. Design a Chat Service (like Facebook Messenger or WhatsApp)

• Focus on real-time messaging and data synchronization across devices.
• Handle high volumes of messages while maintaining low latency.
• Ensure data privacy and security in message transmission.
• Implement features like group chats, media sharing, and read receipts.

High-Level Design: The architecture should include a scalable server infrastructure to handle concurrent users and message traffic.

A real-time messaging protocol like WebSockets can be used for instant communication. Data storage should consider a distributed database system for scalability and quick access. The design should also incorporate a notification system for message alerts across devices.

Key Points to Consider: Pay attention to efficient data routing and message queuing systems. Ensure data consistency and durability in case of network failures. Optimize for low latency in message delivery.

Consider the trade-offs between relational and non-relational databases for storing messages and user data. Security measures like end-to-end encryption are crucial for user privacy.

Check out how to design Messenger.

Question 2. Design a Mass Social Media Service (like Facebook, Twitter, or Instagram)

• Strategies for handling large-scale data and user traffic.
• Implement features like news feeds, post interactions, and multimedia content.
• Consider user authentication and content moderation systems.
• Focus on personalized user experiences and content recommendation algorithms.

High-Level Design: The design should encompass a distributed server architecture to manage high traffic loads. A complex database structure is needed for storing various types of content, user data, and interaction histories. The system should include algorithms for news feed generation and content recommendation, considering user preferences and behavior.

Key Points to Consider: Efficient data indexing and search capabilities are essential. The design should handle the trade-off between data consistency and availability. Scalability is crucial for handling peak loads. Content delivery networks (CDNs) can be used to improve content delivery speeds. Privacy and data security policies are paramount.

Question 3. Design a Social Network and Message Board Service (like Quora, Reddit, or HackerNews)

• User-generated content, community engagement, and content moderation.
• Scalability and efficient search functionality across numerous posts and threads.
• Implement systems for user reputation and content ranking.
• Ensure reliability and consistency in content updates and user interactions.

High-Level Design: The architecture should include components for user management, content storage, and search functionality. A hierarchical data model can be effective for organizing threads and responses. The system should have robust mechanisms for content moderation and spam detection. Integrating a caching system would improve response times for frequently accessed content.

Key Points to Consider: The design must ensure quick access and update times for threads with high user activity.

Scalability is key for handling sudden spikes in traffic. Implementing effective algorithms for content ranking and recommendation based on user activity and preferences is crucial.

Privacy and security features need to be integrated to protect user data.

Question 4. Design a File Sharing Service (like Dropbox, Google Drive, or Google Photos)

• Secure file storage, sharing, and synchronization across multiple devices.
• Handling large file sizes and optimizing for fast upload/download speeds.
• Implement version control and recovery options for files.
• Considerations for user access control and file encryption.

High-Level Design: The service should be built on a cloud-based infrastructure for scalability and accessibility. It should include a file management system for uploading, storing, and retrieving files efficiently. A synchronization mechanism is necessary to keep files updated across devices. The design must incorporate security measures such as encryption and secure authentication.

Key Points to Consider: Focus on optimizing data transfer speeds and minimizing storage costs. Implement a robust system for data backup and recovery. User interface design is crucial for a seamless user experience. The system should support different file formats and sizes. Security and privacy of user data are of utmost importance.

Learn how to design Dropbox.

Question 5. Design a Video Sharing Service (like YouTube, Netflix)

• Manage large-scale video storage and optimize streaming services for different devices.
• Implement user recommendations, content search, and playback quality adjustments.
• Focus on scalable video encoding and transcoding processes.
• Develop strategies for handling peak streaming demands and content delivery.

High-Level Design: A distributed content delivery network (CDN) is essential for efficient video streaming. The system must include components for video storage, transcoding, and streaming.

A recommendation engine based on user preferences and viewing history will enhance user experience. The design should also consider adaptive bitrate streaming for different network conditions.

Key Points to Consider: The architecture must support high bandwidth and storage requirements. Video compression techniques are important to reduce storage and bandwidth costs.

Ensuring low latency and high availability is crucial for user satisfaction. Implementing machine learning algorithms for personalized recommendations will improve user engagement. Security and copyright compliance are also critical considerations.

Learn how to design YouTube.

Question 6. Design a Proximity Service (like Yelp, Nearby Friends, Uber)

• Integrate location-based services and real-time updates.
• Balance privacy concerns with functionality for services reliant on user location.
• Consider efficient geospatial queries and location accuracy.
• Develop strategies for dynamic content based on user location.

High-Level Design: The system should include a geolocation service for tracking and updating user locations.

A scalable database for storing location data and performing geospatial queries is essential. The design must ensure efficient real-time data processing and updating. Implementing user privacy controls and location-sharing settings is vital.

Key Points to Consider: Focus on the accuracy and precision of location data. Scalability is key to handle a large number of concurrent location requests.

Data caching can improve response times for frequent queries. User privacy and data security should be prioritized in the design. Consideration for varying network conditions and GPS availability is important.