The System Design Interview: Explained in 20 Minutes

I still remember my first System Design interview as a young engineer.

It was November of 2012 and I was slated to meet with a hiring leader at Meta's Seattle headquarters (back when it was still called Facebook, and back when this part of the loop was still in person).

And I'll be honest: I was pretty nervous.

Despite having a few years of experience under my belt and possessing a solid understanding of software architecture, System Design was a relatively new ideology.

At that time, the System Design interview focused mainly on sketching high-level architectural diagrams and discussing basic design principles. This was likely because monolithic architectures were the dominant paradigm then, and microservices had not yet emerged. The emphasis was on evaluating your ability to conceptualize how various components fit together, rather than deep dives into scalability, operational complexity, or trade-offs.

Fast forward to 2025, and System Design interviews at top tech companies like Facebook (Meta), Netflix, and Uber are commonplace — and they've evolved significantly. This crucial stage of the hiring loop is now more rigorous, structured, and challenging than ever. These interviews test your ability to think critically, communicate clearly, and design systems that scale and run reliably in production, all while under considerable pressure from seasoned interviewers.

I know this because I've also been on the other side of the interview table.

Over the years, I’ve led hundreds of System Design interviews at Microsoft, Meta, and now Educative. Through these experiences, I’ve gained unique and actionable insights into what interviewers are really looking for today, whether you're a new graduate preparing for your first interview or a senior engineer looking for a change of scenery.

In this guide, I’ll share proven strategies and practical tips to help you approach System Design interviews with confidence and clarity. We’ll cover:

• How the System Design interview has evolved from the early 2000s to today

• Foundational concepts that will be used again and again

• A proven framework (RESHADED) to tackle any System Design problem

• Common interview pitfalls and how to navigate them

• Interview preparation techniques to get your reps in

I’ll try my best to meet you where you are, and provide actionable advice tailored for engineers of all experience levels. So if there's one guide you read as you prepare for your upcoming System Design Interview — let it be this.

I promise you won't regret it.

I. How System Design Interviews Have Evolved#

Before diving head first into strategies and frameworks, it's important to understand how this critical piece of the hiring loop has evolved.

When I first encountered System Design interviews, the process was relatively informal. Interviewers typically asked you to sketch a high-level architecture for a basic web app or database schema. The main goal was to see if you grasped how different modules fit together.

But today, System Design interviews have become far more structured and demanding, especially as modern software increasingly adopts AI-Agentic architectures.

Here’s a deeper look at what specifically has changed:

1. From sketches to detailed designs: Today, you're expected to go beyond vague sketches. Interviewers want detailed discussions about key system components such as databases, caches, load balancers, and queues. They care about why you make certain design choices, not just what those choices are.
   You should be prepared to explore data storage strategies, caching mechanisms, replication methods, consistency models, the underlying algorithms, and more.

2. Trade-offs are critical: No System Design is perfect. In modern interviews, you’re expected to clearly understand trade-offs, such as balancing consistency with availability, or choosing between latency and throughput. Interviewers expect you to weigh pros and cons and justify your decisions. This ability is a core skill for system architects and senior engineers alike.

3. Operational concerns matter: Designing a system that works on paper is not enough. You need to address real-world operational challenges like monitoring the system, handling logging, and recovering from failures.

4. Communication and adaptability: Your ability to clearly explain your reasoning and adapt when requirements change is just as important as the technical solution itself. Interviewers often introduce curveballs mid-discussion to test your flexibility.

To effectively demonstrate your ability to build reliable and scalable systems, you need to make sure you understand — and internalize — the basic concepts behind System Design.

II. Foundational System Design Concepts You Need to Master#

System Design interviews test your grasp of the core building blocks that underpin scalable and reliable systems.

Whether you’re a new graduate or a seasoned engineer, mastering these concepts will work wonders in boosting your confidence and credibility.

Let’s discuss these concepts in detail:

1. Data storage and management#

Data storage and management form the foundation of most systems, making it essential to understand relational and non-relational databases. Relational databases such as MySQL, PostgreSQL, and Microsoft SQL Server provide strong consistency, support complex queries, and enforce ACID transactions. Non-relational databases like MongoDB, Cassandra, and DynamoDB provide greater flexibility and horizontal scalability but often relax consistency to maintain higher availability and partition tolerance.

Data partitioning and sharding become essential for scalability and performance as data volumes grow. Partitioning splits a large table into smaller segments within a single database instance, improving query efficiency by limiting the amount of data scanned. Sharding distributes data across multiple database instances or servers, enabling systems to handle higher loads and provide greater availability. Choosing the right partition or shard keys is crucial for balanced data distribution and efficient access. Implementing proper indexing and query optimization strategies enhances data retrieval performance. A strong grasp of these concepts is vital for designing robust and scalable systems.

2. Caching#

Caching is a vital technique used to improve system performance by storing frequently accessed data closer to the application, which reduces latency and decreases the load on databases. Common caching solutions include in-memory caches such as Redis and Memcached, which provide fast access to data.

For instance, Facebook extensively uses Memcached to cache user session data and newsfeed content, reducing database load and enabling faster response times for billions of daily users. Similarly, despite massive traffic, Twitter caches user timelines to instantly serve personalized feeds.

Distributed caches can scale across multiple servers to handle larger workloads efficiently. One of the key challenges in caching is cache invalidation, which involves strategies like time-to-live (TTL)TTL defines how long data remains in the cache before it expires and is automatically removed, helping manage freshness and memory usage., write-throughData is written to both the cache and the database simultaneously, ensuring consistency but with higher write latency., write-backData is written to the cache first and persisted to the database later, improving write performance but risking data loss on failure., and cache-asideThe application loads data into the cache on demand and writes directly to the database, giving more control but requiring manual cache management. to ensure that stale or outdated data is not served to users. Ensuring cache consistency is also important to accurately reflect recent changes. Understanding these caching strategies and their trade-offs is essential for designing systems that deliver speed and accuracy.

3. Load balancing#

Load balancing is a technique that distributes incoming network traffic across multiple servers to ensure no single server becomes a bottleneck. By efficiently managing workload distribution, load balancing improves system availability and responsiveness.

You should understand common load balancing algorithms, such as:

• Round-robin: Distributes requests evenly across servers,

• Least connections: Sends traffic to the server with the fewest active connections, and

• IP hash: Routes requests based on the client’s IP address.

Health checks are an important feature that enables load balancers to automatically detect and remove unhealthy servers from rotation, ensuring reliability.

For example, Uber handles millions of ride requests daily, particularly during peak hours. Their load balancing system distributes these requests evenly across multiple servers and data centers to maintain low latency and high availability, ensuring riders receive quick matches and drivers get timely requests.

4. Consistency, availability, and partition tolerance#

Consistency, availability, and partition tolerance are core principles in distributed systems that define how systems behave under various conditions. The CAP theorem states that in a network partition, a system must choose between maintaining consistency and ensuring availability. Since partitions are inevitable, understanding this trade-off is critical. The PACELC theorem builds on this by highlighting that even in the absence of partitions, systems must balance latency and consistency. Grasping these trade-offs is key to designing distributed systems that align with real-world needs and limitations.

5. Redundancy and replication#

Redundancy and replication are key techniques for building resilient and fault-tolerant systems. Redundancy involves duplicating critical components or services to eliminate single points of failure, ensuring the system remains operational even if one component fails. Replication involves copying and maintaining data across multiple nodes or regions to improve fault tolerance and read performance.

Different replication models exist, including primary-secondary, where one node handles writes and others handle reads, and multi-leader, where multiple nodes can handle both reads and writes simultaneously.

Replication can be:

• Synchronous, which ensures data consistency by waiting for all copies to update before completing the operation, or

• Asynchronous, which improves performance but may allow temporary inconsistencies.

Understanding the benefits and trade-offs of these models helps you design systems that meet both availability and consistency requirements.

6. Asynchronous processing#

Asynchronous processing plays a key role in designing scalable and decoupled systems. It allows different system components to interact without waiting for immediate responses, which helps improve performance and fault tolerance.

Message queues and publisher-subscriber (pub/sub) systems, such as RabbitMQ, Kafka, and AWS SQS, are common tools for implementing asynchronous communication. These systems enable tasks to be processed independently and support event-driven architectures, making it easier to handle real-time notifications, batch processing, and workflows that require high availability.

Amazon, for example, relies heavily on asynchronous processing in its order fulfillment systems. When a customer places an order, tasks like payment processing, inventory updates, and shipping label generation are queued and processed independently. This decoupling of components allows the system to scale efficiently without blocking user-facing operations.

7. Rate limiting#

Rate limiting is a crucial technique in System Design that controls the number of requests a user or client can make within a given time frame. It helps protect systems from abuse, prevents server overload, and ensures fair user usage. Without proper rate limiting, a surge in traffic, whether accidental or malicious, can overwhelm backend services, degrade performance, or cause outages. Common algorithms like token bucket, leaky bucket, and fixed window are used to enforce limits effectively. Understanding rate limiting is essential for designing resilient, secure, and scalable systems, especially for APIs, authentication services, and public-facing platforms.

8. Content delivery networks (CDNs)#

CDNs are distributed networks of servers designed to deliver content to users based on their geographic location. They improve the performance and reliability of web applications by caching content closer to end users, which reduces latency and decreases bandwidth costs. Popular CDN providers include Akamai, Cloudflare, and AWS CloudFront.

Netflix is a prime example of CDN usage at scale. To deliver smooth, high-quality video streams worldwide, Netflix caches large video files on edge servers close to users in various regions. This reduces the distance data must travel and lowers latency, minimizing buffering and improving playback quality. By offloading traffic from origin servers to these CDN edge nodes, Netflix can reliably serve millions of concurrent streams cost-effectively. If an edge server experiences issues, requests are automatically rerouted to alternate nodes, ensuring uninterrupted viewing.

By offloading traffic from origin servers and distributing content globally, CDNs help ensure faster load times, better user experience, and improved scalability, especially for applications with a large, geographically dispersed user base.

9. Fault tolerance and monitoring#

Fault tolerance and monitoring are essential for designing reliable systems that can continue functioning even when components fail. Fault tolerance involves incorporating redundancy, failover mechanisms, and graceful degradation to ensure the system remains operational during failures. Monitoring complements this by continuously tracking system health, performance metrics, and error rates using tools such as Prometheus, Datadog, or CloudWatch. Effective monitoring enables teams to detect issues early, trigger alerts, and respond quickly to reduce downtime. Fault tolerance and monitoring help maintain high availability, improve the user experience, and support proactive system maintenance.

With a strong grasp of these fundamental concepts, let’s explore a framework that will help you systematically approach and ace System Design interview problems.

III. Applying the RESHADED Framework#

System Design interviews can feel overwhelming without a clear strategy.

To succeed and stand out, following a structured framework that organizes your thinking ensures you address all critical aspects and demonstrates your problem-solving approach.

I recommend using a framework called RESHADED, which breaks the process into simple, manageable steps. Here’s a visual overview of this framework:

Let’s discuss each step in detail:

1. Requirements clarification#

Requirement clarification is the first and one of the most critical steps in any System Design discussion. Your main goal is to clearly define what you are building and why. Start by identifying the functional requirements, which are the core features and behaviors the system must support. They often include user workflows, inputs and outputs, and key use cases.

Next, explore the non-functional requirements, such as expected scale, latency targets, uptime guarantees, and data consistency needs. These determine how the system should perform under real-world conditions.

Be sure to ask clarifying questions about the problem statement. Understand the scope, user expectations, and edge cases. By the end of this step, you should clearly understand the service, its purpose, and the constraints that will shape your design decisions.

2. Estimation#

Estimation focuses on predicting the infrastructure and resources needed to support the system’s expected scale. It helps you quantify the system’s needs regarding servers, storage, bandwidth, and other key components.

Start by asking targeted questions about usage patterns, data volume, and system traffic. Creating solid estimates lays the foundation for a practical and scalable design.

3. Storage schema (data modeling)#

Data modeling is the step where we define how information will be structured and stored within the system. This typically involves identifying the key entities, designing tables or collections, and specifying the fields and relationships between them. For example, in a social media app, entities might include users, posts, comments, and likes. While data modeling is not always required in every System Design interview, especially when time is limited, including it can help clarify how the system will manage and organize data. A clear data model also supports more informed decisions around storage solutions, indexing strategies, and query patterns.

4. High-level design#

The next step is to present a high-level design based on the requirements you identified earlier. Start by outlining the system’s major components and showing how they interact. This often involves drawing a simple block diagram including clients, servers, databases, caches, message queues, and other key elements. This high-level overview helps frame the problem clearly and gives interviewers a mental map of your solution.

5. API design#

This phase focuses on designing the interfaces through which users and other systems interact with different services. These interfaces are typically exposed as API endpoints that map directly to the functional requirements you defined earlier. Each API call represents a specific action or workflow, such as creating a user, retrieving data, or posting content. Well-designed APIs ensure clarity, consistency, and ease of integration, making them critical to the system’s usability and scalability.

6. Detailed design#

The detailed design phase begins by identifying gaps or limitations in your high-level design and refining it into a complete and practical solution. This step involves diving deeper into each component, specifying the technologies, protocols, and architectural patterns to be used. You’ll define how services interact, choose data stores, detail caching layers, and describe communication mechanisms such as queues or APIs. The goal is to finalize all the building blocks and components needed to bring the system to life, ensuring that every part of the design meets requirements and can scale effectively.

7. Evaluation#

The next step is to evaluate your design critically by identifying potential bottlenecks and considering key trade-offs. Look for areas that may become performance or scalability pain points, such as overloaded databases, slow response times, or single points of failure. Address these challenges with techniques like database sharding, introducing caching layers, partitioning services, or scaling components horizontally and vertically.

At the same time, recognize that every design involves trade-offs. Evaluate the pros and cons of your choices, such as consistency vs. availability, latency vs. throughput, or simplicity vs. flexibility. A thoughtful analysis of trade-offs demonstrates your ability to balance competing priorities and design practical, real-world systems. This step strengthens your solution and showcases your critical thinking and engineering judgment.

8. Distinctive components and features#

This step involves identifying the unique challenges of the system you’re designing. While many systems share components like caching or load balancing, standout problems, like YouTube, require specialized solutions for things like video storage, adaptive streaming, CDNs, and real-time recommendations. These add constraints such as large uploads, smooth playback, and personalized content delivery.

Such specialized requirements go beyond basic architecture and demand thoughtful, domain-specific solutions. Recognizing and addressing them early demonstrates your ability to design systems that are scalable and reliable, and tailored to the product’s unique needs.

Advantages of RESHADED#

The RESHADED framework serves as a mental checklist, helping you remember the essential steps to tackle any System Design problem during the interview. It provides a clear path forward, so you never wonder what to do next.

By following this approach, your solution will cover all the foundational elements of good System Design. More importantly, it ensures your design is structured, well-reasoned, and aligned with real-world engineering expectations.

With a solid framework, let’s now understand the common challenges candidates face during System Design interviews and how to overcome them effectively.

IV. Common Pitfalls & How to Avoid Them#

System Design interviews are complex, and even experienced engineers can stumble over certain recurring challenges. Being aware of, and preparing for the following pitfalls, can give you a massive advantage.

Let’s discuss each:

1. Ambiguous or changing requirements: Interviewers may intentionally keep requirements vague or introduce changes mid-discussion to assess your adaptability. When this happens, respond by asking clarifying questions, restating your understanding, and explaining how your design can accommodate the updated requirements. Showing flexibility under changing conditions is a key part of what makes a strong System Designer.

2. Over-engineering or under-engineering: Finding the right level of complexity is critical. Avoid building overly complex solutions that waste resources or too simple ones that fail to meet requirements. Start with a basic design and iterate by adding components only when justified.

3. Time management: With limited interview time, getting lost in details is easy. Use the proven framework to pace yourself, focusing first on the high-level design before diving into specifics. Keep an eye on the clock and communicate your plan.

4. Communication gaps: Effective communication is as important as technical skills. Clearly explain your thought process, assumptions, and trade-offs. Invite feedback regularly to ensure you and the interviewer stay aligned.

5. Lack of trade-off analysis: Many candidates forget to discuss trade-offs central to System Design. Always address the pros and cons of your choices, demonstrating that you understand the impact on scalability, consistency, performance, and maintainability.

6. Neglecting operational concerns: Failing to consider monitoring, alerting, failover, and maintenance can make your design unrealistic. Be sure to include operational strategies to show a complete understanding of running systems in production.

What MAANG Companies Are Actually Looking For#

Spoiler: it isn't your coding ability.

Over time, some of the biggest tech companies have refined their System Design interviews to better evaluate candidates against their unique technical challenges and evolving business needs.

Meta, for instance, may incorporate dynamic constraints and shifting requirements to test a candidate’s adaptability and real-time problem-solving. Uber may have shifted focus toward distributed systems and real-time processing, reflecting their complex, high-throughput platform. Netflix emphasizes designing scalable and resilient systems that handle massive global user loads, aligned with their microservices architecture.

These trends suggest that the top companies continuously tailor interviews to assess core design skills and qualities essential to their engineering cultures.

It's also worth pointing out that it isn't just the System Design Interview that's changed — tech hiring as a whole looks a lot different now than it did back in 2015

Checkpoint: Read-Heavy vs. Write-Heavy Systems#

Thinking about system architecture in terms of their read & write demands is a favorite prompt among MAANG interviewers.

Before an interviewer cares about shards or queues, they want to know whether a system's workload is read-heavy or write-heavy.

• Read-heavy systems spend most of their time serving fetches—think Netflix streaming a movie or Facebook showing the next News Feed story. Here, latency and fan-out dominate, so you reach for CDNs, caching layers, and read replicas.

• Write-heavy systems absorb a nonstop flow of state changes—Uber logging driver pings or WhatsApp ingesting billions of messages. Durability, ordering, and back-pressure drive the design, so you lean on partitioned logs, batching, and idempotent writes.

The graphic below places a handful of top tech companies along that continuum.

V. Learn from My Mistakes — and Prepare Like a Pro#

At this point, you might be wondering how that very first system design interview I had with Facebook actually went.

And it may surprise you to learn that it did not go particularly well.

Despite spending weeks preparing, I didn't walk into the interview with a clear framework for approaching problems. I remember the interviewer being a lot more "hands on" than usual, which made it difficult to gauge whether my efforts were heading in the right direction.

But more importantly? I spent my time preparing for the wrong things.

Fortunately, the market was a bit less competitive back then and I still managed my way through it. But I can't imagine how much worse it might have gone had I taken this approach in 2025.

Success in the modern System Design interview does not come by chance; it requires focused preparation and consistent practice. (Important note for

those in need of a quick fix: this crash course is probably your best bet if you're short on time.)

Here are some other best practices and recommended resources to supplement your interview prep:

1. Practice real System Design problems: Regularly work through common System Design problems like:

   1. designing a URL shortener

   2. designing a messaging system like WhatsApp

   3. designing a newsfeed system

2. Study System Design fundamentals: Deepen your understanding of core concepts such as databases, caching, load balancing, and distributed systems.

3. Review existing architectures: Analyze the architecture of popular systems (e.g., Twitter, Netflix, Uber). Understanding real-world systems helps bridge theory and practice.

4. Participate in mock interviews: You can utilize online mock interviews to simulate real interview conditions. The feedback you receive from mock interviews on your communication and design approach is invaluable for improvement.

5. Develop communication skills: Practice explaining your design clearly and concisely. Focus on storytelling, guiding the interviewer through your thought process logically.

6. Use visual aids: Get comfortable drawing clear diagrams to illustrate your design. Visual representation helps convey complex ideas efficiently.

7. Invest in a crash course: This is a condensed version of our flagship course, Grokking the Modern System Design Interview for Engineers & Managers, designed to help you build confidence, master fundamentals, and perform under pressure. Perfect for software engineers and managers aiming to ace high-stakes interviews at top tech companies.

VI. Further Reading#

A few months into my new life at Facebook, I ran into the interviewer who led my System Design interview.

Despite shaking my hand and being friendly... it was clear that he had no idea who I was.

But he did say this: "turns out you were good enough!"

By going the extra mile to review the following resources, I'm confident you won't just be good enough — you'll be truly great:

• Grokking the Modern System Design Interview: This course provides a modular approach to mastering System Design interviews. It teaches you to design complex microservice-based systems, analyze project requirements, and prepare for common interview questions. The course features an adaptive framework used by engineers and managers, enabling you to tackle any System Design problem confidently.

• Distributed Systems for Practitioners: This course introduces the core principles of distributed systems, explaining what they can and cannot do through simple examples and diagrams. It covers key algorithms, clarifies concepts like consistency, explores common challenges, and encourages thoughtful trade-off analysis.

• System Design Deep Dive: Real-World Distributed Systems: This course explores how large-scale systems are designed and operated to meet demanding service-level goals, using real-world examples from companies like Apple, Google, Meta, and Amazon. You’ll learn the modern System Design, understand key trade-offs, and study timeless design principles through systems that have proven their value in production.

Stay curious, keep practicing, and don’t hesitate to seek feedback to learn from each experience. With dedication and the right mindset, I’m confident you can ace your next System Design interview — and take your career to the next level.