Arslan Ahmad

The Complete Guide to Ace the System Design Interview

The 7–step process to answer any system design interview question.

What is a system design interview?

System design interview questions are asked to understand how a candidate thinks about complex problems, how well they communicate their ideas, and how well they collaborate with others.

The questions asked in system design interviews are based on large-scale real-world problems. Answering these questions demonstrates the candidate's ability to think creatively and work in a team.

Why is a system design interview important?

The purpose of a system design interview is to assess your ability to design and implement a system from start to finish. System design interview allows you to demonstrate your knowledge, your problem-solving skills, your ability to take a problem and break it down into smaller parts, and your ability to work in a team.

How to prepare for system design interviews?

  • The best way to get the most out of your preparation is by practicing.
  • Read books and online courses on system design interviews.
  • Practice with friends and colleagues.
  • Practice with a mentor; it may be an experienced developer or senior engineer on your team or someone else who can give you feedback about what you got right or wrong in a mock interview session and help you improve for your next interview.
  • Practice mock interviews using one of the many resources available online.
  • To ensure you don't forget what you have learned, keep track of everything in a notebook or spreadsheet and review it regularly.

How to answer a system design question?

System design interview questions focus on abstract problem-solving rather than your specific knowledge of a programming language or technology stack. As such, they're good indicators of how well you can design and solve large-scale problems without having all the information in front of you.

The key to answering system design interview questions is understanding the big picture of how your system works.

When you're asked about the design of a particular system, take time to understand what the interviewer wants to know about this system and why it's important for them.

How do you get started on a system design interview question?

Here is a 7-step process that helps you create a solution to a system design problem:

  • Step 1: Requirements clarification
    When you are asked to design a system for a problem, the first thing that you should do is understand the problem. You need to understand what the users of your system will do, what they are trying to accomplish, and how does your solution help them achieve their goals? Understand all of the constraints of the system. You need to know things like, how many users are there in total? Will they all use the system at once, or will they access it individually?

  • Step 2: Back-of-the-envelope estimation
    It is always a good idea to estimate the scale of the system you are going to design. This will also help later when you focus on scaling, partitioning, load balancing, and caching.

  • Step 3: System interface definition
    Define what APIs are expected from the system. This will establish the exact contract expected from the system and ensure that you haven't gotten any requirements wrong.

  • Step 4: Defining the data model
    Defining the data model will clarify how data will flow between different system components. Later, it will guide for data partitioning and management.

  • Step 5: High-level design
    Draw a block diagram with 5–6 boxes representing the core components of our system. You should identify enough components that are needed to solve the actual problem from start to end.

  • Step 6: Detailed design Dig deeper into two or three major components; the interviewer's feedback should always guide you to what parts of the system need further discussion. You should present different approaches, their pros and cons, and explain why you will prefer one approach over the other.

  • Step 7: Identifying and resolving bottlenecks Try to discuss as many bottlenecks as possible and different approaches to mitigate them.

Topics to Master for System Design Interviews

As we've journeyed through the world of system design interviews, we've established their importance and understood their purpose. Now, let's delve into the meat of the matter: the topics you need to master to ace these interviews. Think of these topics as your toolkit. The more tools you have and the better you understand how to use them, the better you'll be at crafting solutions to the challenges presented in system design interviews.

1. Basics of System Design

The first tool in your toolkit is an understanding of the basics of system design. It's like learning to draw. Before you can paint a masterpiece, you first need to master basic shapes. Similarly, before you can design complex systems, you need to understand the fundamental concepts.

A. Large-Scale Systems and Architecture: At the heart of system design is the ability to design large-scale systems. These could be systems that serve millions of users, handle vast amounts of data, or provide crucial functionality for a business. Understanding how these systems are architected, how they scale, and how their various components work together is fundamental to system design.

B. Key System Design Concepts: There are key concepts that underpin system design. These include concepts like scalability, reliability, availability, consistency, and load balancing. Having a solid understanding of these concepts will allow you to design systems that not only meet the given requirements but are also robust and resilient.

Here are the short description of the key system design fundamentals:

  1. Scalability: It's like the "growth capacity" of your system. Scalability refers to the system's ability to handle increased load and grow over time. Imagine your system is a bus, and as more passengers (users or data) come in, you need to ensure your bus can handle it.

  2. Reliability: This is about "trustworthiness". A reliable system functions correctly and consistently under specified conditions. It's like an old friend you can always count on - your system should be the same for your users.

  3. Availability: This is about "uptime". Availability refers to the system being accessible and operational when users need it. If your system is a shop, you want to make sure it's open when customers come to visit.

  4. Consistency: This is about "sameness". Consistency means the data in the system remains the same across all the components in all the cases. It's like a menu in a restaurant chain - you want to offer the same dishes in all branches.

  5. Efficiency: This is about "resourcefulness". An efficient system performs its functions in the most optimal way, often with least resources possible. Think of it as fuel efficiency in a car - the less fuel you use for a distance, the more efficient your car is.

  6. Robustness: This is about "resilience". Robustness is the ability of a system to cope with errors during execution and cope with erroneous input. It's like a tree that withstands a storm.

  7. Security: This is about "safety". Security involves protecting the system from malicious attacks and unauthorized access. It's like having a good lock on your door, keeping your house safe.

  8. Maintainability: This is about "easy-care". A maintainable system is designed in such a way that it's easy to update and upgrade. It's like a well-organized toolbox - when a tool needs to be replaced, it can be done quickly and without fuss.

  9. Modularity: This is about "compartmentalization". In a modular system, the whole system is divided into separate modules, each handling a specific functionality. It's like a puzzle, where each piece fits together to form the whole picture.

  10. Fault Tolerance: This is about "forgiveness". A fault tolerant system continues to operate even if part of the system fails. It's like a plane that continues flying even if one engine fails.

2. Common System Design Patterns

Once you've grasped the basics, it's time to add some more tools to your toolkit. These come in the form of system design patterns. Just like patterns in knitting guide you on how to create different types of stitches, system design patterns guide you on how to solve common problems in system design. They provide proven solutions that you can adapt to fit your particular situation.

A solid understanding of common system design patterns like Primary-Replica, Peer-to-Peer, Publisher-Subscriber, and more will be a significant advantage during your interviews. These patterns provide blueprints that you can build upon to design your system. Here are the most common patterns:

  1. Primary-Replica: This is the "leader-follower" pattern. The primary server handles all the write operations and updates the replica servers, which handle the read operations. If the primary server fails, one of the replicas steps up to become the new primary. It's like a team with a leader and followers, making sure there's always a backup plan.

  2. Peer-to-Peer (P2P): Think of this as a "group of friends". In this pattern, all nodes in the network participate equally, sharing resources directly without a centralized coordination. It's great for file sharing systems, kind of like how friends share stuff among themselves.

  3. Publisher-Subscriber: This is the "newspaper" pattern. Here, publishers produce data and subscribers consume it. The publishers don't need to know who their subscribers are, and vice versa. It's like subscribing to a newspaper—you get the news without knowing who printed it.

  4. Sharding: Consider this the "pie slice" pattern. Sharding involves breaking your data into smaller parts, or "shards", each held on a separate database server. It's like slicing a pie where each slice can be served independently, helping to boost performance and adding redundancy.

  5. MapReduce: This is the "divide and conquer" pattern. It splits a big data problem into subproblems, processes them in parallel (map), and then combines the results (reduce). It's like having a big cleanup task, you'd split it amongst your friends, and then gather the trash bags together at the end.

  6. Eventual Consistency: This is the "patience pays" pattern. It assures that, if no new updates are made to a given data item, eventually all accesses to that item will return the most recent update. It's like gossip in a group of friends, eventually everyone ends up with the latest news.

  7. Circuit Breaker: Think of this as the "safety switch". It monitors for failing service calls and once the failures reach a certain threshold, the circuit breaker trips, and all further calls to the service fail immediately. It's like an electrical circuit breaker in your home, protecting your appliances from damage.

3. Databases and Storage Systems

In the realm of system design, databases and storage systems are the treasure chests that hold the valuable data your system will process. They are the foundations upon which your system will be built, and understanding them is crucial.

Understanding different types of databases (like SQL and NoSQL), their strengths and weaknesses, and when to use each type is key. Similarly, understanding different storage systems (like block, file, and object storage) and how to choose between them based on factors like speed, cost, and data type is also essential.

Here are some of the top types of databases you'll encounter:

  1. Relational Databases (RDBMS): These are the "organized lockers" of data storage. Data in an RDBMS is structured in tables, and relationships can be formed between different tables. RDBMS have fixed database schema. Examples include MySQL and PostgreSQL. It's like keeping your stuff neatly organized in lockers, where each locker is a table.

  2. NoSQL Databases: These are the "free spirits". NoSQL databases are non-tabular and store data differently than relational tables. They are designed for large scale data storage and are flexible in storing structured, semi-structured, or unstructured data. MongoDB and Cassandra are popular examples. Imagine it as a big box where you can dump anything you want, without worrying about organization.

  3. In-Memory Databases: These are the "speedy ones". In-memory databases store data in the memory (RAM) of the server instead of on disk, making data access incredibly fast. Redis is a well-known in-memory database. It's like keeping your most frequently used items right on your desk instead of in your locker for quick access.

  4. Graph Databases: These are the "web weavers". Graph databases use graph structures to store, map and query relationships. They are excellent for analyzing interconnected data. Neo4j is a popular graph database. It's like creating a family tree, where relationships are as important as the individual people.

  5. Key-Value Stores: Key-value stores are the "buddy system" of databases. Imagine walking into a huge warehouse filled with millions of boxes. Now, if each box had a unique name (key), and you knew exactly what name corresponds to the box you need, you could find your box (value) in no time. That's exactly what key-value stores do! In this type of database, data is stored as a collection of key-value pairs where each unique key is associated with a value. Keys act as identifiers to find the data quickly. It's like a dictionary, where each word (key) has a corresponding meaning (value).

  6. Document Databases: These are the "record keepers". Document databases store data in documents similar to JSON objects. Each document can contain pairs of fields and values, and each value can be of various types. MongoDB is a famous document database. It's like having a filing cabinet where each drawer has different documents with various data.

  7. Column Store Databases: These are the "column kings". Column-oriented databases store data by columns instead of rows. This makes querying and performing operations on a specific field across all rows faster. Cassandra and HBase are examples. It's like storing data vertically in a spreadsheet, focusing on columns rather than rows.

Top system design interview questions for software developers

Because system design interviews can cover a wide range of topics, it's important to prepare by researching potential questions beforehand.

Here are some of the most common questions asked during a system design interview:

  1. Design URL shortening service.
  2. Design a social network like Facebook, Instagram, or Twitter.
  3. Design a global chat service like Facebook Messenger or WhatsApp.
  4. Design a global video streaming service like YouTube or Netflix.
  5. Design a ride-hailing service like Uber or Lyft.
  6. Design a web crawler.
  7. Design Typeahead search.
  8. Design Ticketmaster.
  9. Design a key-value store.
  10. Design an API rate limiter.
  11. Design a global file storage and sharing service like Dropbox or Google Drive.
  12. Design a distributed messaging system.
  13. Design an elevator system.
  14. Design a parking lot system.
  15. Design a game of chess.
  16. Design a movie ticket booking system.
  17. Design a library management system.
  18. Design an e-commerce store like Amazon.

Discussing Trade-offs

As a senior engineer, presenting trade-offs in a system design interview is highly significant as it demonstrates your depth of understanding and maturity in design. Here’s are a few important trade-offs that you can discuss during the interview:

Common distributed system algorithms

As a senior software engineer, familiarizing yourself with famous distributed system algorithms is highly important. Here is a list of distributed system algorithms that can be used to solve real-world problems:

  1. CAP and PACELC Theorems
  2. Bloom Filter
  3. Merkle Tree
  4. Heartbeat
  5. Consistent Hashing
  6. Gossip Protocol
  7. Read Repair

This added layer of complexity in the interviews for principal software engineers is reflective of the pivotal role they play in driving innovation and technological excellence within the company.

Common problems during a system design interview

  • Don't be afraid to ask questions. It's important to remember that you should always feel comfortable asking the interviewers any question you may have. This is an opportunity for you to get clarification on anything that's unclear or confusing, and it will also help set up a flow of communication between yourself and your interviewer(s).
  • Don't be intimidated by the interviewer(s). Several interviewees feel nervous about being put on the spot. If this happens to you, remember that it is part of the process: everyone gets butterflies before an interview! Try not to let nerves get in your way when answering questions - instead, focus on giving great responses.
  • Don't be afraid to ask for clarification if something isn't clear enough in terms of what exactly is being asked. Ask questions about requirements and constraints. Questions like what types of data do we need? How much data are we expecting? Where does this data come from? What do we know about our users' behavior (and what don't we know)?

Top Resources for System Design Interviews

Let's take a look at some of the famous resources that can help you ace system design interview:

Online Courses and Tutorials

Online courses and tutorials provide an interactive and structured approach to learning system design.

  • "Grokking the System Design Interview": This course by Design Gurus is highly respected in the tech community for its comprehensive content and practical approach. It covers a wide range of system design topics and includes real-world examples and solutions to common system design problems.

  • Coursera "Software Design and Architecture Specialization": This series of courses dives deep into software architecture and design principles, focusing on techniques and methods that help you design software systems more effectively.

  • Grokking Microservices Design Patterns, to learn microservices design patterns for designing scalable, resilient, and more manageable systems.


Books can be incredible resources for learning about system design. They offer in-depth knowledge, insightful examples, and often years of expertise condensed into a few hundred pages. Here are a few top picks that could act as your tour guides.

"Designing Data-Intensive Applications" by Martin Kleppmann: This book is a treasure trove of knowledge about designing systems that handle large amounts of data. It dives deep into topics like data models, storage engines, indexing, data replication, partitioning, transactions, and more.

"Clean Architecture: A Craftsman's Guide to Software Structure and Design" by Robert C. Martin: In this book, you'll explore the principles of software architecture, how to create flexible and scalable software systems, and much more. It's like a comprehensive guide to building sturdy and effective systems.

Blogs and Websites

Finally, we have the vast and endless realm of blogs and websites. These can offer nuggets of wisdom, practical tips, and a wealth of information, often free of charge.

High Scalability: This blog covers all things related to scalability, from architecture to databases to best practices. It also features real-world examples of scalable systems.

The System Design Primer on GitHub: This repository provides an overview of system design topics and includes numerous resources for further learning.

Engineering Blogs: Check the software engineering blogs of Uber, Netflix, Design Gurus, [Pinterest]

Ready to ace your next tech interview?

In this article, we have discussed the process of system design interviews for software developers. Take a look at Grokking the System Design Interview for system design interview questions like:

  1. Designing a file-sharing service like Google Drive or Dropbox.
  2. Designing a popular messaging service like Facebook Messenger.
  3. Designing popular social network sites like Twitter or Facebook.
  4. Designing a global video streaming service like YouTube.
  5. Designing a global ride-hailing service like Uber.

To learn software architecture and practice advanced system design interview questions take a look at Grokking the Advanced System Design Interview.

Read more about system design and coding interviews:
[1] Mastering the System Design Interview: A Complete Guide
[2] Top LeetCode Patterns for FAANG Coding Interviews
[3] System Design Interviews: What distinguishes you from others?

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