System Design Interview: A Step-By-Step Guide

Summary

This video script outlines a structured framework for system design interviews, emphasizing the importance of understanding the problem, proposing a high-level design, and conducting a deep dive into potential issues. It suggests allocating time wisely across four key steps: problem understanding, high-level design, deep dive, and wrap-up, to ensure a comprehensive and impactful interview within a typical 45-60 minute session.

Takeaways

• 📝 The importance of following a framework in system design interviews to manage stress and time effectively.
• 🔍 A structured interview helps in asking the right questions and focusing on what matters most in the design process.
• 🛠️ The framework consists of four main steps: Understanding the problem, high-level design proposal, deep dive into design, and wrap-up.
• ⏰ Time allocation is suggested for each step, with a focus on the core 35-45 minutes of the interview for in-depth discussion.
• 🤔 The necessity to ask clarifying questions to fully understand the problem and establish the design scope.
• 📝 The significance of understanding user needs, system features, and non-functional requirements like scale and performance.
• 🔑 The role of APIs in establishing a contract between end users and backend systems, and the importance of adhering to RESTful conventions.
• 📊 The use of a high-level design diagram as a blueprint to verify that the design meets all feature requirements.
• 🗂️ The consideration of data models and schemas in the design process, especially their impact on performance at scale.
• 🔑 The deep dive step is crucial for identifying potential problems, proposing solutions, and discussing trade-offs.
• 🔍 The importance of 'reading the room' during the interview to pick up on interviewer cues and address concerns effectively.
• 🔚 The wrap-up step involves summarizing the design and asking questions about the company to show interest.

Q & A

Why is it important to follow a framework during a system design interview?

A framework is important because interviews are stressful and time-limited. Without a structured approach, it's easy to waste time on irrelevant details, and an unstructured interview can be difficult for the interviewer to follow. A framework provides a time-tested structure that guides the candidate to ask the right questions and focus on the right aspects of the design.

What are the four steps in the proposed system design interview framework?

The four steps are: 1) Understand the problem and establish design scope, 2) Propose high-level design and get buy-in, 3) Design deep dive, and 4) Wrap up.

How should the time be allocated during a typical 45-60 minute system design interview session?

The suggested time allocation is about 5 minutes for step 1, 20 minutes for step 2, 15 minutes for step 3, and 5 minutes for step 4, with the first 5 minutes for introduction and the last 5 for Q&A.

Why is it a red flag to jump into a solution without first understanding the problem in a system design interview?

Jumping into a solution without fully understanding the problem can lead to addressing the wrong issues or proposing a design that doesn't meet the actual requirements. It's crucial to clarify the requirements and understand the system's purpose, users, and necessary features before proposing a solution.

What types of questions should be asked during step 1 to clarify the requirements for a system design?

Questions should focus on clarifying why the system is being built, identifying the target users, and determining the priority of features to be included. It's also important to understand non-functional requirements like scale and performance.

Why is it suggested to start with APIs when developing a high-level design in step 2?

Starting with APIs is beneficial because they establish a contract between the end users and the backend systems. They define the input parameters and output responses, ensuring that the design meets the functional requirements gathered during the problem understanding phase.

What is the significance of discussing the data model and schema during the high-level design phase?

Discussing the data model and schema is crucial because it impacts the performance of the system, especially at scale. It involves decisions about data access patterns, read/write ratios, and potentially the choice of database, which can significantly affect the system's efficiency.

What is the purpose of the 'design deep dive' step in the framework?

The purpose of the 'design deep dive' is to identify potential problem areas, propose solutions, and discuss trade-offs. It demonstrates the candidate's ability to handle non-functional requirements and think critically about the design's challenges.

How can a candidate effectively communicate their design decisions during the deep dive section?

A candidate can effectively communicate by clearly articulating the problem, proposing multiple solutions, discussing the trade-offs of each solution using supporting numbers, and then selecting a solution to discuss in detail with the interviewer.

What should be the focus during the wrap-up step of the system design interview framework?

The focus during the wrap-up should be on summarizing the unique aspects of the design and ensuring that all parts of the design are complete end-to-end. It's also important to leave time to ask the interviewer questions about the company.

Why is it recommended to maintain a list of discussion points while developing the high-level design?

Maintaining a list of discussion points helps to keep the design process organized and ensures that all important aspects are covered. It also prevents the candidate from getting too detailed too early, which could lead to overlooking the overall design.

Outlines

00:00

📚 System Design Interview Framework Overview

This paragraph introduces a structured framework for system design interviews, emphasizing its importance in managing stress and time efficiently. The framework consists of four steps: understanding the problem, proposing a high-level design, a deep dive into the design, and a wrap-up. The speaker suggests time allocations for each step and stresses the need for clarity in requirements and non-functional requirements like scale and performance. The importance of rough calculations for understanding system scale is also highlighted.

05:02

🔍 Developing a High-Level System Design

The second paragraph delves into the process of creating a high-level system design. It starts with establishing APIs based on functional requirements and then moves on to designing a high-level diagram that includes components like load balancers, services, and data storage. The paragraph advises against diving into details too early and suggests maintaining a list of discussion points. It also touches on data modeling, the importance of choosing the right databases and indexing options, and the need for a thorough review of the design before moving on to the deep dive.

🚀 System Design Deep Dive and Problem-Solving

This paragraph focuses on the deep dive phase of the system design interview, where potential issues are identified, and solutions are discussed with trade-offs. It emphasizes the importance of working closely with the interviewer and using non-functional requirements to make the design interesting. The paragraph provides a mini-guideline for framing discussions, including articulating the problem, proposing solutions, discussing trade-offs, and choosing a solution. It also advises on using 'read-the-room' skills to address the interviewer's concerns and suggests focusing on the top 2 or 3 issues due to time constraints.

🏁 Wrapping Up the System Design Interview

The final paragraph discusses the wrap-up phase of the system design interview, suggesting a brief summary of the design, highlighting unique aspects, and leaving time for questions about the company. It concludes by promoting a weekly system design newsletter for further insights into large-scale system designs, trusted by 200,000 readers, and invites viewers to subscribe for more information.

Keywords

💡System Design Interview

A system design interview is a critical part of the hiring process for software engineering roles, where candidates are assessed on their ability to design large-scale systems. In the video, the framework for such interviews is discussed, emphasizing the importance of structure and clear communication to demonstrate a candidate's capability within a limited time frame.

💡Framework

A framework in this context refers to a structured approach or set of guidelines that helps in organizing thoughts and actions systematically. The video script outlines a specific framework consisting of four steps to follow during a system design interview, which aids in managing time effectively and addressing key aspects of the problem.

💡High-Level Design

High-level design is an initial, broad overview of a system's architecture, which includes the main components and their interactions without delving into the specifics. In the script, it is suggested to propose a high-level design to establish an agreement with the interviewer on the overall structure before moving into more detailed aspects.

💡APIs

APIs, or Application Programming Interfaces, are sets of routines, protocols, and tools for building software applications. The script highlights the importance of defining APIs as part of the high-level design, as they establish the contract between end users and the backend systems, and are crucial for satisfying functional requirements.

💡Non-Functional Requirements

Non-functional requirements are aspects of a system that define its quality, such as performance, scalability, and usability. The video emphasizes the significance of these requirements in system design interviews, especially when scaling the system to handle a large number of users or data volume.

💡Scale

Scale refers to the ability of a system to handle growth, whether in terms of user numbers, data volume, or transaction rates. The script discusses the importance of considering scale when designing systems, as it introduces unique challenges and affects the choice of technologies and architectural decisions.

💡Load Balancer

A load balancer is a component of a distributed system that distributes network or application traffic across multiple servers to ensure no single server bears too much demand. In the script, it is mentioned as a typical starting point for a high-level design diagram, indicating its role in managing traffic and enhancing system performance.

💡Data Modeling

Data modeling is the process of creating a representation of data objects, the relationships among them, and the rules governing these relationships. The script mentions that at scale, data modeling can significantly impact system performance, and it is a key part of the high-level design process.

💡WebSocket

WebSocket is a communication protocol that provides full-duplex communication channels over a single TCP connection, enabling real-time data transfer between client and server. The script discusses WebSocket as a common solution for two-way communication, while also noting the challenges of operating it at scale.

💡Deep Dive

A deep dive in the context of the video refers to an in-depth analysis or discussion of specific aspects of the system design. The script describes this as a critical step in the interview framework where candidates demonstrate their ability to identify potential issues, propose solutions, and discuss trade-offs.

💡Trade-Offs

Trade-offs are the balancing acts between different aspects of a design, often involving choosing between one feature's strength and another's. The script advises discussing trade-offs when proposing solutions during the deep dive section, to highlight the decision-making process in system design.

💡QPS

QPS stands for Queries Per Second, a measure of throughput for a server or database system. The script uses the term in an example to illustrate the challenges of handling high write rates, such as in a location database for a service like Google Maps.

💡NoSQL Database

NoSQL databases are non-relational databases that are designed to handle large volumes of data with flexible schema. The script suggests considering a NoSQL database as a solution to handle high write rates, indicating its utility in specific scalability scenarios.

Highlights

The video introduces a system design interview framework used in the authors' books.

The framework aims to provide structure in interviews, helping candidates showcase their abilities effectively within a short time.

A structured interview makes it easier for interviewers to follow the candidate's thought process.

The framework consists of four steps: understanding the problem, proposing a high-level design, a deep dive into the design, and wrapping up.

The framework is suitable for a typical 45-60 minute system design interview session.

Time allocation for each step is suggested, with 5 minutes for understanding the problem, 20 minutes for high-level design, 15 minutes for deep dive, and 5 minutes for wrap-up.

In the problem understanding step, candidates should ask clarifying questions to fully grasp the requirements and prioritize features.

Non-functional requirements like scale and performance are crucial for system design interviews.

Candidates should perform rough estimates to understand the system's scale and potential challenges early on.

APIs are central to the high-level design, establishing a contract between end users and backend systems.

A high-level design diagram serves as a blueprint, verifying that the design meets all feature requirements.

Data storage layer is introduced in the high-level design, without specifying the exact database technology at this stage.

During the deep dive, candidates should identify potential problem areas and propose solutions with trade-offs.

The deep dive section is where non-functional requirements make the problem interesting and challenging.

Candidates should use 'read-the-room' skills to pick up on interviewer cues and address concerns.

In the wrap-up step, candidates should summarize the design and ask the interviewer questions about the company.

The video concludes by promoting a weekly system design newsletter for further insights into large-scale system designs.

Transcripts

In this video,  

we talk about the system design interview  framework that we used in our books.

We explain why you might want to consider  using something similar when you interview.

Let’s first talk about why we  might want to follow a framework.

Interviews are stressful.

There is very little time to  show off what we are capable of.

Without any structure, it is easy to waste  precious time on things that don’t matter.

An unstructured interview makes it  difficult for the interviewer to follow.

Our framework provides a time-tested structure.

It is simple and powerful. It leads us to ask the  right questions and focus on the right things.

Here are the 4 steps in our framework.

Step 1 - Understand the problem  and establish design scope.

Step 2 - Propose high-level design and get buy-in

Step 3 - Design deep dive

Step 4 - Wrap up

This framework works well for a typical 45-60  minute long system design interview session.

Usually, the first 5 mins is an  introduction, and the last 5 is Q&A.

The meat of the interview  is only about 35-45 mins.

We suggest allocating about 5 minutes to step 1,  

20 mins to step 2, 15 mins to  step 3, and 5 mins to step 4.

Keep in mind this is just a rough  guideline. Feel free to adjust as needed.

Let’s take a closer look  at each of the four steps.

Step 1 - Understand the problem  and establish design scope.

System design questions are usually open-ended.

Sometimes they are presented in  a way that is deliberately vague.

This tests our ability to organize our  thoughts and focus on what is important.

It is our job to ask as many questions as  necessary to understand the problem fully.

It is a red flag to jump right into a solution  without first understanding what we are building.

What questions should we ask?

Our goal is to clarify the requirements.

We want to understand why  we are building the system,  

who the users are, and what  features we need to build.

For example, if we are asked to design a chat app,  

it is important to recognize that there are many  different types of chat apps in the marketplace.

There are one-on-one and small-group  chat apps like WhatsApp, office chat  

apps like Slack, or group chat apps like Discord.

They have different design  challenges and constraints.

The goal is to understand the features  we are building in priority order.

We should focus on the top few features to build.

Make sure the interviewer  agrees to the feature list.

It is also important to ask a series of questions  to clarify the non-functional requirements.

For system design interviews, we suggest  focusing on scale and performance.

These non-functional requirements are what  make our design unique and challenging.

For example, designing a Twitter clone  to support a few hundred users is easy,  

while designing it for hundreds of  millions of users with some popular  

accounts having millions of followers  is interesting and challenging.

The more senior the role is, the more important it  

is for us to demonstrate our ability to  handle the non-functional requirements.

To help us get a sense of the scale of  the system and the potential challenges  

and bottlenecks, we might do some rough  back-of-the-envelope calculations here.

Keep in mind that we have yet to design anything,  so the math we do here is a rough estimate.

The goal is to get a general sense of the scale.

We want to get the order of magnitude right.

This step should take about 5 minutes.

At the end, we should have  a short list of features to  

design for, along with a few important  non-functional requirements to satisfy.

For step 2 of our framework, we aim to  develop a high-level design and reach  

an agreement with the interviewer on the design.

For most designs, we would suggest a  top-down approach and start with the APIs.

The APIs establish a contract between  the end users and the backend systems.

It should be clear after gathering the  requirements what APIs we would need.

Unless it is specified otherwise, we  should follow the RESTful convention.

Define each API’s input parameters  and output responses carefully.

Take the time to carefully review the APIs.

Verify that they satisfy  the functional requirements.

Equally important to remember.

Do not introduce APIs that have nothing  to do with the functional requirements.

An additional consideration on API.

Some designs might call for two-way  communication between client and server.

In this scenario, Websocket  is a common solution here.

Be mindful that a socket service  like websocket is stateful.

It is quite challenging to operate at scale.

If the scale is high, be prepared  to discuss how we would manage a  

WebSocket deployment in the deep dive section.

Once we have established the APIs  between the client and the server,  

the next step is to lay out  the high-level design diagram.

The diagram is the blueprint of the  overall design that we can refer back to.

We should use it to verify that the design  satisfies all the feature requirements end-to-end.

For many designs, it starts with  a load balancer or an API gateway.

Behind that are the services  that would satisfy the feature  

requirements we established  earlier with the interviewer.

Many services require some form of persistence.

This is where we would round out the design  by introducing the data storage layer.

It is usually not necessary to specify the  exact database technology to use at this stage.

This should be deferred to the  deep dive section if necessary,  

and only after we have designed the data schema.

For example, for a map service like Google Maps,  

the client often needs to send  frequent GPS updates to the server.

We would include in our design  a location data store that a  

location update service would write to.

Repeat the steps above and complete the high-level  design diagram for all the major features.

Here is a pro tip.

While developing the high-level design,  maintain a list of discussion points for later.

Resist the temptation to dig  into too much detail too early.

Do not dig ourselves into a hole before  we have a full picture of the design.

The last step of the high-level design  is to hash out the data model and schema.

Here we should discuss the data access  patterns and the read/write ratio.

At scale, data modeling could significantly  impact the performance of the design.

If it is simple, also discuss the databases to  choose, and maybe discuss the indexing options.

Here we should make some judgment calls.

If the data modeling is the key part of  the design to satisfy the non-functional  

requirements, we might want to defer  the discussion to the deep dive section.

When we are done with the high-level design,  take a step back and review the design.

Make sure each feature is complete end-to-end.

Here we reach the third step of  the framework - design deep dive.

The goal of this section is to demonstrate  that we could identify areas that could  

potentially be problematic and come up  with solutions and discuss trade-offs.

We should work with the interviewer  closely to decide what to discuss in depth.

Deep dive is where non-functional  requirements make the problem interesting.

The higher the level, the more  important this section is.

The section is really open-ended.

There is no one-size-fits-all approach.

Here is where the ability to  “read-the-room” is useful.

Sometimes the interviewer’s body  language would give away clues  

that they are dissatisfied with  certain aspects of the design.

It is important to pick up these clues  and make sure the issues are addressed.

One way we could approach  it is by asking questions.

We could list out the reasons for  choosing a particular solution  

and ask if they have any questions or concerns.

Once we pick out a problem  or two to dive deeper into,  

we should come up with multiple solutions  and discuss the trade-offs for each option.

We could use the following mini  guidelines when framing the discussion.

First, we should clearly articulate the problem.

For example, for designing Google  Maps, the write QPS at 1 M/sec to  

the location database is too high  for a single database to handle.

Next, we come up with at least two solutions.

Continuing with the example above, we  could propose to reduce the location  

update frequency per user, or choose a NoSQL  database that could handle the write rate.

Third, we discuss the trade-offs of the solutions.

Remember to use numbers to back up our design.

Finally, we pick a solution and  discuss it with the interviewer.

Repeat this for other problems.  In a typical interview,  

we should only have time to dive  deeper into the top 2 or 3 issues.

Lastly, we have reached the last step - wrap-up.

We suggest spending a few  minutes summarizing the design.

Here we should focus on the parts that  are unique to the particular situation.

Keep this short and sweet.

Leave enough time at the end of the interview to  ask the interviewer questions about the company.

That’s it on the system  design interview framework.

We hope you find it useful.

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