System Design Interview Guide for Backend Engineers | Medium Prob

Apr 8, 2024
Prepare with a medium-probability system design strategy for backend engineers. Enhance your ability to develop robust, scalable systems.
90% of backend devs feel unprepared for their upcoming backend interviews, at big tech companies like Google or Meta. The main reason being, it remain unclear which kind of backend interview questions will come up. An often overlooked yet common component of the hiring process, is the system design interviews.
If you are likely to face one varies widely between companies, roles, and levels of seniority.
That’s why reliably mastering system design interviews requires more than just technical knowledge; it demands a tailored interview prep approach, to avoid wasting time on it or getting lost in the breadth and depth of the topic.
Through this guide, I equip you with a comprehensive system design interview preparation strategy tailored for your individual profile and the companies you are interviewing with.
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Your Assessment Results

Based on your responses, our algorithm indicates a medium probability of encountering system design interviews during your backend interview process. As a backend engineer, it's likely that you'll face both high-level and low-level design questions, ranging from theoretical generic designs to complex real-world applications.
Real-world high-level design questions are inspired by actual systems and challenge you to consider technical and architectural nuances alongside user experience. For example, you might be asked to design a system akin to Dropbox, assessing your ability to navigate data storage, synchronization, and user-centric features like ease of use and accessibility.
Low-level design questions come in two forms: generic and real-world. Generic questions require you to architect complex system components from scratch, such as designing a Content Delivery Network (CDN). Conversely, real-world low-level questions involve intricate details of existing systems, like developing a file synchronization service within a system similar to Google Docs. These questions focus on a deep dive into the specific implementation details of known systems, including algorithms, data structures, and interfaces.
In summary, your interview as a backend engineer could encompass a mix of high-level and low-level design challenges across both generic and real-world scenarios. Given your role as a skilled technical contributor, you should be prepared to engage in detailed discussions on advanced algorithms and the overarching design of complex systems.
Naturally, you might be skeptical of a result generated by a seemingly opaque process. Allow me to explain the factors that influenced this outcome.

Probability of Encountering a System Design Interview

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The likelihood of encountering a standardized system design interview is primarily influenced by two factors:
First, the tier of the company you are interviewing with plays a significant role. Small to mid-sized companies, including startups, are least likely to have a standardized hiring process that includes a formal system design interview. At the other end of the spectrum, large tech companies, often summarized by the acronym FAANG, frequently incorporate system design interviews into their hiring process. For example, Netflix engineering manager interviews are highly likely to include system design rounds.
The second factor is your level of seniority. While junior positions across various software-related roles are unlikely to require system design interviews, the probability increases significantly from mid-level positions onwards. In particular, technical engineering managers and those in higher positions are very likely to face system design and software architecture interviews.

Most Common Types of System Design Interview Questions

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As you’ve probably already realized, the pool of potential questions is indefinite. However, I’ve developed a methodology to categorize these questions along two axes. Questions may target either high-level or low-level designs. High-level design questions focus on the architectural aspects of large systems, while low-level design questions delve into the detailed technical specifics and component-level considerations of systems.
The second axis assesses whether the systems in question are existing real-world systems or more generic, somewhat hypothetical constructs.
From these two axes, four quadrants emerge, allowing us to categorize all questions and then map the likelihood of these questions appearing in system design interviews by role.
Examples of system design questions in these quadrants include:
  • High-Level Design of a Generic System: Design a Vending Machine
  • Low-Level Design of a Generic System: Design a CDN
  • High-Level Design of a Real-World System: Design Dropbox
  • Low-Level Design of a Real-World System: Design a File Sync Service (as found in Dropbox)

Expected Level of System Complexity

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Within each quadrant where a system design interview question may fall, there's another important dimension to consider, which I want you to be aware of: the complexity of the systems relative to the role and seniority of candidates.
In my methodology, questions are categorized into five levels of complexity, where 1 represents the least complex and 5 the most complex. As your seniority increases, so does the complexity of the systems you'll discuss, although this complexity tends to plateau at certain levels, particularly in leadership roles.
The advantage of also clustering questions by complexity level is that it makes it easier to prioritize the types of questions you are most likely to encounter during your interview. This approach helps in building an effective preparation strategy, where tackling the most complex questions first is not recommended.
I use this knowledge to shield my coachees from frustration, ensuring a smooth learning experience and fostering personal growth.

Your Best Preparation Strategy

Understanding what to expect from the system design interview is useful, but the real value lies in deriving actionable insights from this understanding. To that end, I'll provide you with a study plan tailored to your professional background and target companies. This approach ensures that you focus on the interview questions for backend software engineers that are most likely to be asked, allowing you to strategically prepare for the highest probability scenarios first.
I regularly advise my students to first understand what constitutes an exceptional interview performance and the common challenges in distributed systems. Following that, we build foundational design and architecture knowledge from the ground up. This involves starting with individual components, progressing to features, and eventually mastering the design of complete systems. This structured methodology ensures thorough preparation for your interviews.
With this guide, you can get started right away. Assuming you are working full-time and managing personal responsibilities, this plan is designed to keep you effectively engaged for about four weeks. Here’s what you should focus on:

Study the System Design Interview Framework

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To effectively communicate your design, it's best to adhere to a standardized framework consisting of six key steps:
  • Requirements Engineering
  • Reasonable Capacity Estimation
  • API Design
  • Data Model
  • High Level Architecture
  • Design Discussion

Study Computer Science Fundamentals

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Refresh the computer science fundamentals that commonly drive discussions.
  • Horizontal scalability
  • Microservice architecture
  • ACID properties of transactions
  • PACELC theorem (extends CAP)
  • Consensus Algorithms
  • Network Partitions and Handling Failures

Study System Design Components

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Deepen your understanding of the most common system components to effectively integrate them into software architectures. By thoroughly studying these components, you will be able to justify your choices based on their advantages and disadvantages.
  • Load Balancer
  • API Gateway
  • Microservice
  • Message Queue
  • Relational Database
  • Non-relational Database
  • CDN Service
  • Caching Service

Study Supporting Features Independently

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Study how to independently draw and explain supporting features used across different systems (like a search engine in Netflix). This will enhance your agility in architecting unfamiliar systems on the spot.
A good starting point for your profile would include:
  • Search engine
  • Recommendation engine
  • User management
  • Analytics
  • Notification service

Study Systems Type by Type

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Study types of systems rather than individual famous implementations This approach will allow you to adapt more flexibly to unexpected questions.
Real-world high level system architectures you are very likely to encounter:
  • Messengers (e.g., WhatsApp, Signal)
  • Ticketing systems (e.g., RedBus, Ticketmaster, BookMyShow)
  • Accommodation platforms (e.g., Airbnb,
  • Streaming platforms (e.g., Netflix, YouTube, Spotify)
  • Coding platforms (e.g., Topcoder, Codechef, Hackerrank)
  • Question-and-answer platforms (e.g., Quora)
Low Level component architectures (real-world and generic):
  • Reviews
  • News feed
  • Like/dislike button
  • Latency Management System
  • Recommendation system
  • Payment Processing
  • Payment module
  • Concurrent Hashmap
  • CDN Service
  • Distributed Caching


Mastering backend engineering interviews at major tech companies like Google or Meta involves more than deep technical knowledge; it requires a strategic and customized preparation plan. This guide has offered you a detailed roadmap, considering the diverse and often unpredictable nature of system design interview questions specific to different companies, roles, and levels of seniority.
With this preparation strategy, you're equipped with the insights needed to anticipate the kinds of questions you may encounter, from high-level architectural discussions to detailed component design. Begin your preparation journey with our free assessment test to fine-tune your approach based on your unique profile. Move forward with confidence, and be ready to excel in your upcoming system design interviews.

Fast-Track Your Preparation

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If you're short on time and eager to get started, check out my highly-rated Udemy course. Designed based on the most common needs from my tech interview coaching clients, this course condenses the essential knowledge into less than 5 hours of video content. It's a fast track to mastering what you need to know.