LLD interview expectations - Architecture Diagram

System Overview - LLD interview expectations

This system represents the typical flow and components involved in a Low-Level Design (LLD) interview process. The key requirements include clear communication between the candidate and interviewer, structured question handling, and feedback collection to evaluate design skills effectively.

Architecture Diagram

User (Candidate)
   |
   v
Load Balancer
   |
   v
API Gateway
   |
   v
Interview Service <--> Design Question DB
   |
   v
Feedback Service
   |
   v
Storage (Feedback DB)

Cache (for frequently asked questions) connected to Interview Service

Components

User (Candidate)

user

Person participating in the LLD interview

Load Balancer

load_balancer

Distributes incoming interview requests evenly to backend services

API Gateway

api_gateway

Routes requests to appropriate services and handles authentication

Interview Service

service

Manages interview session, question delivery, and candidate responses

Design Question DB

database

Stores design questions and related metadata

Cache

cache

Speeds up access to frequently asked design questions

Feedback Service

service

Collects and processes interviewer feedback

Storage (Feedback DB)

database

Stores feedback and evaluation results

Request Flow - 13 Hops

User (Candidate) → Load Balancer

Load Balancer → API Gateway

API Gateway → Interview Service

Interview Service → Cache

Cache → Interview Service

Interview Service → Design Question DB

Design Question DB → Interview Service

Interview Service → User (Candidate)

User (Candidate) → Interview Service

Interview Service → Feedback Service

Feedback Service → Storage (Feedback DB)

Feedback Service → Interview Service

Interview Service → User (Candidate)

Failure Scenario

Component Fails:Cache

Impact:Interview Service experiences slower question retrieval due to cache miss; increased load on Design Question DB

Mitigation:System falls back to querying Design Question DB directly; cache is asynchronously rebuilt

Architecture Quiz - 3 Questions

Which component routes the candidate's request to the correct service?

A API Gateway

B Load Balancer

C Interview Service

D Cache

Design Principle

This architecture demonstrates separation of concerns by dividing responsibilities among services, uses caching to improve performance, and includes fallback mechanisms to handle component failures gracefully.

Practice

1. What is the main focus of a Low-Level Design (LLD) interview?

easy

A. Choosing cloud providers and infrastructure

B. Estimating system capacity and scaling

C. Designing detailed components and their interactions

D. Writing complex SQL queries

Solution

1. Step 1: Understand LLD interview scope

   LLD interviews focus on designing small parts of a system clearly and in detail.

2. Step 2: Compare options with LLD focus

   Estimating capacity and scaling, choosing cloud providers and infrastructure, and writing database queries relate to other areas, not the main focus of LLD interviews.

3. Final Answer:

   Designing detailed components and their interactions -> Option C

4. Quick Check:

   LLD = detailed component design [OK]

Hint: LLD = detailed design of small system parts [OK]

Common Mistakes:

• Confusing LLD with high-level system design
• Thinking LLD focuses on infrastructure
• Mixing LLD with database query writing

2. Which of the following is the correct way to represent a relationship in a class diagram during an LLD interview?

easy

A. Using arrows to show inheritance and lines for associations

B. Using SQL queries to define relationships

C. Using cloud icons to represent services

D. Using flowcharts to show data flow

Solution

1. Step 1: Identify class diagram conventions

   Class diagrams use arrows for inheritance and lines for associations between classes.

2. Step 2: Eliminate unrelated options

   SQL queries, cloud icons, and flowcharts are not used to represent class relationships in LLD diagrams.

3. Final Answer:

   Using arrows to show inheritance and lines for associations -> Option A

4. Quick Check:

   Class diagram = arrows + lines [OK]

Hint: Class diagrams use arrows and lines for relationships [OK]

Common Mistakes:

• Confusing class diagrams with flowcharts
• Using database or cloud symbols incorrectly
• Ignoring inheritance arrows

3. Consider this simplified class design snippet in an LLD interview:

class User {
  int id;
  String name;
  List<Order> orders;
}

class Order {
  int orderId;
  double amount;
}

What is the relationship between User and Order?

medium

A. Inheritance

B. Aggregation

C. Composition

D. No relationship

Solution

1. Step 1: Analyze the class fields

   User has a list of Orders, meaning User contains Orders but Orders can exist independently.

2. Step 2: Determine relationship type

   Since Orders can exist without User, this is aggregation, not composition or inheritance.

3. Final Answer:

   Aggregation -> Option B

4. Quick Check:

   User "has" Orders = Aggregation [OK]

Hint: List field means aggregation, not inheritance [OK]

Common Mistakes:

• Confusing aggregation with composition
• Thinking it's inheritance due to class names
• Ignoring independence of Order objects

4. You designed a class diagram but forgot to show the multiplicity on associations. What issue might this cause in an LLD interview?

medium

A. Ambiguity about how many objects relate to each other

B. Syntax error in the diagram

C. The system will not compile

D. No impact, multiplicity is optional

Solution

1. Step 1: Understand multiplicity role

   Multiplicity shows how many instances of one class relate to another, clarifying design details.

2. Step 2: Consequence of missing multiplicity

   Without it, the design is unclear about object counts, causing ambiguity.

3. Final Answer:

   Ambiguity about how many objects relate to each other -> Option A

4. Quick Check:

   Missing multiplicity = unclear relationships [OK]

Hint: Multiplicity clarifies object counts in relationships [OK]

Common Mistakes:

• Thinking diagram syntax breaks without multiplicity
• Assuming multiplicity is always optional
• Confusing multiplicity with inheritance

5. During an LLD interview, you are asked to design a simple library system with Books and Members. Which design choice best follows LLD interview expectations?

hard

A. Design a single class Library with all methods and no separation

B. Use complex inheritance hierarchies for Book types without explaining choices

C. Focus only on database schema without class diagrams

D. Create classes Book and Member with clear attributes and a borrowing relationship using aggregation

Solution

1. Step 1: Identify good LLD design practices

   LLD expects clear classes with attributes and simple relationships like aggregation.

2. Step 2: Evaluate options against LLD expectations

   Creating classes Book and Member with clear attributes and a borrowing relationship using aggregation matches best by defining classes and relationships clearly. A single class lacks separation, database schema skips class diagrams, and unexplained complex inheritance overcomplicates without clarity.

3. Final Answer:

   Create classes Book and Member with clear attributes and a borrowing relationship using aggregation -> Option D

4. Quick Check:

   Clear classes + simple relationships = LLD [OK]

Hint: Clear classes + simple relationships = good LLD design [OK]

Common Mistakes:

• Overcomplicating with inheritance
• Ignoring class separation
• Skipping diagrams and explanations