System design interview structure in HLD - System Design Exercise

Design: System Design Interview Structure

Includes the interview phases, key questions to ask, and evaluation criteria. Excludes specific system design problems or technologies.

Functional Requirements

FR1: Provide a clear step-by-step approach to conduct a system design interview

FR2: Include key phases such as requirement gathering, high-level design, detailed design, and scaling discussion

FR3: Ensure the structure supports evaluating candidate's problem-solving and communication skills

FR4: Allow flexibility for different system design problems and candidate experience levels

Non-Functional Requirements

NFR1: The interview should fit within a 45-minute to 1-hour time frame

NFR2: The structure must be simple enough for interviewers and candidates to follow easily

NFR3: Focus on clarity and logical progression without overwhelming technical jargon

NFR4: Support both remote and in-person interview formats

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

❓ Question 5

Key Components

Requirement gathering and clarification

High-level system architecture

Component design and data modeling

Scaling and bottleneck identification

Trade-off analysis and alternatives

Design Patterns

Divide and conquer approach

Iterative refinement

Use of diagrams and sketches

Ask clarifying questions

Summarize and confirm understanding

Reference Architecture

Interview Structure
+-------------------------+
| 1. Requirement Gathering |
+-----------+-------------+
            |
            v
+-------------------------+
| 2. High-Level Design     |
+-----------+-------------+
            |
            v
+-------------------------+
| 3. Detailed Design       |
+-----------+-------------+
            |
            v
+-------------------------+
| 4. Scaling Discussion    |
+-----------+-------------+
            |
            v
+-------------------------+
| 5. Wrap-up and Feedback  |
+-------------------------+

Components

Requirement Gathering

Interview conversation

Understand what the system should do and clarify ambiguities

High-Level Design

Whiteboard or digital drawing tool

Outline main components and their interactions

Detailed Design

Diagramming and discussion

Design key components, data models, and APIs

Scaling Discussion

Verbal reasoning

Identify bottlenecks and propose scaling strategies

Wrap-up and Feedback

Conversation

Summarize design and provide candidate feedback

Request Flow

1. Interviewer presents the problem and candidate asks clarifying questions.

2. Candidate gathers and confirms requirements with interviewer.

3. Candidate sketches high-level architecture showing main components.

4. Candidate explains detailed design of critical components and data flow.

5. Candidate discusses how to scale the system and handle failures.

6. Interviewer and candidate summarize the design and discuss trade-offs.

7. Interviewer provides feedback and concludes the interview.

Database Schema

Not applicable for interview structure design.

Scaling Discussion

Bottlenecks

Candidate runs out of time before completing design

Candidate focuses too much on details too early

Interview lacks clear structure causing confusion

Candidate struggles to communicate ideas clearly

Solutions

Allocate time per phase and gently guide candidate if needed

Encourage starting with high-level design before details

Use a consistent interview framework for clarity

Encourage candidate to verbalize thought process and ask questions

Interview Tips

Time: Spend 5-10 minutes on requirement gathering, 10-15 minutes on high-level design, 15-20 minutes on detailed design and scaling discussion, and 5-10 minutes on wrap-up and feedback.

Clarify requirements before jumping into design

Start with a simple high-level architecture

Iteratively add details and justify choices

Discuss scaling and trade-offs realistically

Communicate clearly and ask clarifying questions

Practice

1. What is the first step you should take when starting a system design interview?

easy

A. Discuss the deployment strategy

B. Start coding the solution immediately

C. Draw the final architecture diagram

D. Understand the problem requirements clearly

Solution

1. Step 1: Identify the initial focus in system design

   The first step is to understand the problem requirements clearly to know what needs to be built.

2. Step 2: Avoid premature actions

   Jumping to coding or drawing diagrams without understanding leads to wasted effort and confusion.

3. Final Answer:

   Understand the problem requirements clearly -> Option D

4. Quick Check:

   First step = Understand requirements [OK]

Hint: Always clarify requirements before designing [OK]

Common Mistakes:

• Starting design without clarifying requirements
• Jumping to coding too early
• Ignoring problem constraints

2. Which of the following is the correct order of steps in a typical system design interview?

easy

A. Design components -> Write code -> Understand requirements -> Define APIs

B. Understand requirements -> Define APIs -> Design components -> Discuss trade-offs

C. Write code -> Define APIs -> Understand requirements -> Discuss trade-offs

D. Discuss trade-offs -> Write code -> Design components -> Understand requirements

Solution

1. Step 1: Recall the logical flow of system design

   The correct flow starts with understanding requirements, then defining APIs, designing components, and finally discussing trade-offs.

2. Step 2: Eliminate incorrect sequences

   Writing code is usually not part of the initial design steps, so options with coding first are incorrect.

3. Final Answer:

   Understand requirements -> Define APIs -> Design components -> Discuss trade-offs -> Option B

4. Quick Check:

   Logical design flow = Understand requirements -> Define APIs -> Design components -> Discuss trade-offs [OK]

Hint: Follow problem -> APIs -> design -> trade-offs order [OK]

Common Mistakes:

• Starting with coding instead of design
• Skipping API definition
• Discussing trade-offs too early

3. During a system design interview, you propose a caching layer to improve performance. Which of the following is the most likely benefit you should mention?

medium

A. Increases database storage capacity

B. Eliminates the need for load balancers

C. Reduces database load and decreases response time

D. Automatically scales the number of servers

Solution

1. Step 1: Understand caching purpose in system design

   Caching stores frequently accessed data closer to the user, reducing database queries and improving response time.

2. Step 2: Evaluate other options

   Increasing storage, removing load balancers, or auto-scaling servers are unrelated to caching benefits.

3. Final Answer:

   Reduces database load and decreases response time -> Option C

4. Quick Check:

   Caching benefit = Reduced load and latency [OK]

Hint: Cache reduces DB hits and speeds up responses [OK]

Common Mistakes:

• Confusing caching with storage increase
• Thinking caching replaces load balancers
• Assuming caching auto-scales servers

4. You designed a system with a single database server. During the interview, the interviewer points out a potential bottleneck. What is the most likely issue?

medium

A. Single point of failure and limited scalability

B. Too many load balancers causing delays

C. Excessive caching leading to stale data

D. Overuse of microservices causing complexity

Solution

1. Step 1: Analyze single database server drawbacks

   A single database server can fail and cannot handle very high traffic, causing bottlenecks.

2. Step 2: Check other options for relevance

   Load balancers, caching, and microservices issues are unrelated to having a single DB server.

3. Final Answer:

   Single point of failure and limited scalability -> Option A

4. Quick Check:

   Single DB = bottleneck and failure risk [OK]

Hint: Single DB risks failure and limits scale [OK]

Common Mistakes:

• Blaming load balancers for DB bottleneck
• Confusing caching issues with DB limits
• Ignoring single point of failure risk

5. In a system design interview, after presenting your architecture, the interviewer asks you to handle sudden traffic spikes. Which approach best addresses this?

hard

A. Implement auto-scaling with load balancers to add/remove servers dynamically

B. Use a single powerful server to handle all traffic

C. Remove caching to reduce complexity

D. Store all data in a single database to simplify writes

Solution

1. Step 1: Understand traffic spike handling

   Auto-scaling with load balancers allows the system to add or remove servers based on traffic, handling spikes efficiently.

2. Step 2: Evaluate other options

   A single server cannot handle spikes well; removing caching or using one DB limits performance and scalability.

3. Final Answer:

   Implement auto-scaling with load balancers to add/remove servers dynamically -> Option A

4. Quick Check:

   Traffic spikes = Auto-scaling + load balancers [OK]

Hint: Use auto-scaling and load balancers for spikes [OK]

Common Mistakes:

• Relying on one server for high traffic
• Removing caching unnecessarily
• Ignoring scalability needs