What is asked in design interview?

In a design interview, you’re asked to propose high-level architectures and strategies for building scalable, reliable, and efficient software systems.

Instead of focusing on coding specifics, interviewers want to see how you think about the “big picture”—how components fit together, how data flows, and how the system adapts as it grows or faces failures.

Common Areas Explored

1. Requirements and Constraints
Interviewers typically start by clarifying what the system should do. You’ll need to determine:

• Functional Requirements: What features must be supported? For example, a social media feed or video recommendations.
• Non-Functional Requirements: Consider performance goals, uptime targets, and how quickly the system must respond.

2. High-Level Architecture
You’ll outline the system’s building blocks—frontends, APIs, databases, caches, queues, load balancers, and more. The interviewer wants to see if you can piece together a blueprint that’s both logical and maintainable.

3. Scalability and Performance
System design interviews often involve very large scales. You might discuss:

• Load Balancing: Distributing incoming requests evenly.
• Sharding and Partitioning: Splitting data to handle massive traffic or storage loads.
• Caching Strategies: Reducing database load and speeding up responses.

4. Data Storage and Retrieval
Expect questions about choosing the right type of database—SQL vs. NoSQL—and how you handle indexing, replication, or backup strategies. You’ll explain why a particular storage solution fits the given scenario.

5. Reliability, Availability, and Fault Tolerance
Interviewers may ask how you’d ensure the system stays up despite component failures. Discuss:

• Redundancy and Failover: Keeping multiple servers or services ready to step in if one fails.
• Disaster Recovery Plans: Quickly restoring data and services after major outages.

6. Security and Compliance
You should show awareness of:

• Authentication and Authorization: How users prove who they are and what they can access.
• Data Protection: Using encryption and secure channels to guard against breaches.

7. Trade-Offs and Alternatives
System design is about making informed choices. You’ll be asked why you prefer certain architectures or technologies and how you’d handle limitations or evolving requirements. Talking through pros and cons demonstrates depth of understanding.

8. Communication Skills and Problem-Solving Approach
Throughout the discussion, the interviewer observes how you articulate your thought process and adapt to feedback. Clear explanations, logical reasoning, and the ability to break down complex problems into manageable parts are crucial.

Example Questions in Design Interviews

• Design a URL shortener like Bitly.
• Architect a messaging system like WhatsApp.
• Build a video streaming service like Netflix.
• Create an e-commerce system like Amazon.
• Design a social media feed like Twitter.

How to Prepare and Improve

Study Foundational Concepts:
Learn the fundamentals of load balancing, caching, database indexing, replication, and partitioning. Understand different system architecture patterns like monoliths, microservices, and event-driven designs.

Practice With Real-World Scenarios:
Try designing a URL shortener, a streaming platform, or a chat application. Work through the reasoning, sketch a diagram, and consider how to scale your solution to millions of users.

Use Guided Resources for a Structured Approach:
To gain confidence and clarity on system design principles, leverage resources from DesignGurus.io:

• Grokking the System Design Interview: A step-by-step guide covering common system design challenges.
• Grokking System Design Fundamentals: Builds your baseline knowledge and strengthens your grasp of essential concepts.
• Grokking Microservices Design Patterns: Focuses on distributed systems, patterns, and best practices for scaling microservices.

Refine Communication Skills:
Practice explaining your designs clearly, using simple language and diagrams. Show logical progressions from requirements to solution, and be ready to discuss trade-offs as they come up.

In essence, a design interview tests how you think about building large-scale systems, handle complexity, address real-world challenges, and communicate effectively.

By understanding key topics, practicing scenario-based questions, and learning from structured resources, you can enter these interviews prepared and confident.