System design interview structure in HLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the first step in a system design interview?

Understanding and clarifying the requirements clearly before starting the design.

beginner

Why is it important to ask clarifying questions during a system design interview?

To ensure you understand the problem scope and constraints, which helps in designing an appropriate solution.

intermediate

What does 'high-level design' mean in the context of system design interviews?

It means outlining the main components and their interactions without going into low-level details.

beginner

Name two common components you might include in a high-level system design diagram.

Clients (users or devices) and servers (application servers, databases).

intermediate

What is the purpose of discussing trade-offs during a system design interview?

To show your understanding of different design choices and their impact on scalability, reliability, and cost.

What should you do immediately after hearing the system design problem?

A Write code

B Start drawing the architecture

C Ask clarifying questions

D Discuss trade-offs

Asking clarifying questions helps you understand the problem fully before designing.

Which of the following is NOT typically part of a high-level design?

A Main system components

B External system interactions

C Data flow between components

D Detailed database schema

Detailed database schema is a low-level detail, not part of high-level design.

Why is scalability important in system design?

A To handle increasing user load smoothly

B To reduce initial development time

C To make the system look complex

D To avoid writing documentation

Scalability ensures the system can grow and handle more users or data without failure.

What is a common first step after clarifying requirements?

A Write test cases

B Define system components

C Deploy the system

D Optimize code

Defining components helps organize the system structure early on.

Which trade-off might you consider in system design?

A Latency vs. consistency

B Color vs. font size

C Number of developers vs. salary

D Keyboard layout vs. mouse type

Latency vs. consistency is a classic trade-off in distributed system design.

Describe the typical structure of a system design interview from start to finish.

Think about the logical steps you take when solving a design problem.

Explain why trade-offs are important in system design interviews and give an example.

Consider how different choices affect system behavior.

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