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Demystifying System Design Interviews

System Design interviews do not have to be hard if you know the fundamentals. Follow along and get better at systems thinking.
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This is a free introductory course into system design interviews. They can be daunting, but they don’t have to be. Let’s look at how you can ace your next system design interview.

My goal with this series is to simplify the foundations of a system design interview for everyone. Whether you’re preparing for your first system design interview or brushing up on your skills, this course will guide you through the essential concepts and practical applications.

Building this course has taken many months of effort outside my day job and my role as a parent and husband. It’s an ongoing effort and I make time for this so that it may benefit others.

So all I request from you is to give me a shout-out on social media and Buy me a coffee if you can.

Course Overview

This comprehensive course is designed for anyone preparing for system design interviews or wanting to understand how large-scale systems work. No prior experience with distributed systems is required—we’ll build your knowledge step by step.

Here’s what we’ll cover:

1. Introduction to System Design

Start your journey by understanding what system design interviews are all about, why organisations conduct them, and how to prepare effectively. We’ll demystify the process and set you up for success.

Get started with the Introduction →

2. Foundational Concepts

Before diving into complex systems, you need to understand the building blocks. This section covers:

  • Domain Name System (DNS): How the internet’s phonebook works and why it matters
  • Client-Server Architecture: Understanding the fundamental communication model
  • Network Protocols: HTTP, REST, and modern API design
  • Data Storage Fundamentals: How data is organised, stored, and retrieved

These concepts form the foundation upon which all distributed systems are built.

Explore Foundational Concepts →

3. Non-Functional Requirements

Understanding what makes a system “good” beyond just functionality:

  • Scalability: Designing systems that grow with demand
  • Availability: Keeping systems running when it matters most
  • Reliability: Building trust through consistent performance
  • Performance: Optimising for speed and efficiency
  • Consistency: Managing data across distributed systems

Learn about Non-Functional Requirements →

4. Core Technologies

Deep dives into the essential components of distributed systems:

  • Databases: Choosing the right data store for your needs, understanding SQL vs NoSQL, and managing data at scale
  • Load Balancers: Distributing traffic intelligently across your infrastructure
  • Distributed Cache: Speeding up your applications with intelligent caching strategies
  • Distributed Monitoring: Observing and debugging complex distributed systems
  • Key-Value Stores: Building and understanding simple yet powerful data structures
  • Content Delivery Networks (CDN): Serving content quickly across the globe

Each topic includes practical examples, diagrams, and real-world applications.

Dive into Core Technologies →

5. Practical Case Studies

Apply what you’ve learnt to real-world scenarios. These case studies walk you through designing complete systems from scratch, covering requirements gathering, architecture decisions, and trade-offs.

URL Shortener: Design a service like bit.ly - a perfect introduction to system design interviews covering hashing, databases, and scalability.

Start with the URL Shortener →

How to Use This Course

  1. Follow the order: Each section builds on previous knowledge
  2. Take your time: System design is about understanding trade-offs, not memorising solutions
  3. Draw diagrams: Visual thinking is crucial in system design
  4. Ask questions: Challenge assumptions and explore alternatives
  5. Practice: Apply concepts to real-world systems you use daily

What You’ll Gain

By the end of this course, you’ll be able to:

  • Confidently approach system design interview questions
  • Identify and articulate trade-offs between different architectural choices
  • Design scalable, reliable, and efficient distributed systems
  • Communicate technical decisions clearly and effectively
  • Understand how popular services (like Twitter, YouTube, or WhatsApp) work under the hood

Ready to begin? Let’s start with the Introduction to System Design!

Content Delivery Network (CDN)

Why does YouTube load so quickly no matter where you are in the world? How can Netflix stream 4K video to millions of users simultaneously? The answer: Content Delivery Networks (CDNs). CDNs are distributed networks of servers that cache and deliver content from locations close to users. They’re essential for any service that serves static content (images, videos, CSS, JavaScript) to a global audience. What You’ll Learn In this section, we’ll explore: ...

Key-Value Store

Key-value stores are the simplest form of NoSQL databases, yet they power some of the most sophisticated systems on the internet. From caching to session storage to distributed coordination, understanding how to design a key-value store is fundamental to system design. This isn’t just a theoretical exercise—designing a key-value store is a popular system design interview question because it touches on so many important concepts: hashing, partitioning, replication, consistency, and more. ...

Databases

Databases are the heart of most systems. They’re where your precious data lives, and choosing the right database—and designing it properly—can make or break your system’s performance and reliability. But here’s the thing: there’s no one-size-fits-all database solution. SQL or NoSQL? Relational or document-based? Strong consistency or eventual consistency? The answer is always: “It depends.” What You’ll Learn In this section, we’ll explore everything you need to know about databases for system design interviews: ...

Load Balancers

Imagine thousands of users trying to access your website simultaneously. How do you ensure no single server gets overwhelmed whilst others sit idle? That’s where load balancers come in—they’re the traffic controllers of the internet. Load balancers are crucial for building scalable, highly available systems. They’re one of the first components you’ll add when scaling from one server to many, and understanding them is essential for any system design interview. ...

Foundational Concepts

Before we dive into designing complex distributed systems, we need to establish a solid foundation. These fundamental concepts are the building blocks that every system designer must understand. Think of this section as learning the alphabet before writing essays. You wouldn’t try to design a scalable web application without understanding how the internet routes requests, right? What You’ll Learn In this section, we’ll cover the essential concepts that underpin all distributed systems: ...

Non-Functional Requirements

In system design, it’s not enough to build something that just “works.” Your system needs to work well, reliably, and at scale. That’s where non-functional requirements come in. Whilst functional requirements tell you what your system should do, non-functional requirements define how well it should do it. Should it handle a million users? Should it stay online 99.99% of the time? Should it respond in under 100 milliseconds? These are the questions that separate a toy project from a production-ready system. ...

Distributed Cache

Caching is one of the most powerful techniques for improving system performance. When done right, it can dramatically reduce latency and lighten the load on your databases. In a distributed system, caching becomes even more critical—and more complex. In this section, we’ll explore: Why caching matters: Understanding the performance benefits and use cases Writing policies: How to keep your cache and database in sync Eviction strategies: Managing limited cache space effectively Distributed cache architecture: Sharding, replication, and consistency Cache invalidation: Keeping your data fresh and avoiding stale reads Whether you’re designing a high-traffic web application or optimising database queries, understanding distributed caching is essential for modern system design. ...

Distributed Monitoring

Once your system is distributed across multiple servers, data centres, or even continents, a new challenge emerges: how do you know what’s happening? Is everything running smoothly? Where is the bottleneck? Which component just failed? Distributed monitoring is the art and science of observing complex systems. It’s your eyes and ears in production, helping you detect problems before users notice them and debug issues when they inevitably occur. What You’ll Learn In this section, we’ll explore: ...

URL Shortener

Designing a URL shortener (like bit.ly or TinyURL) is one of the most popular system design interview questions—and for good reason. It’s simple enough to explain in a minute but complex enough to explore deep system design concepts. This seemingly simple service—taking a long URL and returning a short one—touches on databases, caching, scalability, API design, and more. It’s the perfect introduction to practical system design. What You’ll Learn In this comprehensive case study, we’ll design a complete URL shortening service from scratch: ...

Introduction to System Design