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HLDsystem_design~25 mins

What high level design encompasses in HLD - System Design Exercise

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LearnWhyDeepArchPracticeChallengeDesignRecallScale
Design: High Level Design Overview
In scope: system components, interactions, data flow, technology choices. Out of scope: detailed code, database schema, deployment specifics.
Functional Requirements
FR1: Define the main components of a system
FR2: Show how components interact
FR3: Outline data flow between components
FR4: Identify key technologies and protocols
FR5: Provide a clear, simple architecture diagram
Non-Functional Requirements
NFR1: Design must be understandable by non-technical stakeholders
NFR2: Focus on system structure, not detailed implementation
NFR3: Must support scalability and maintainability
NFR4: Avoid low-level code or database schema details
Think Before You Design
Questions to Ask
❓ Question 1
❓ Question 2
❓ Question 3
❓ Question 4
❓ Question 5
Key Components
User Interface (UI)
API Gateway or Load Balancer
Application Servers or Services
Databases or Data Stores
Cache systems
External services or third-party APIs
Design Patterns
Client-Server pattern
Layered architecture
Microservices vs Monolithic
Event-driven communication
Caching strategies
Reference Architecture
  +-------------+       +----------------+       +-------------+
  |   Clients   | <---> | API Gateway /   | <---> | Application |
  | (Web/Mobile)|       | Load Balancer  |       | Servers     |
  +-------------+       +----------------+       +-------------+
                                   |                      |
                                   v                      v
                            +-------------+        +-------------+
                            |   Cache     |        |  Database   |
                            +-------------+        +-------------+
                                   |
                                   v
                          +------------------+
                          | External Services |
                          +------------------+
Components
Clients
Web browsers, Mobile apps
Users interact with the system through these interfaces
API Gateway / Load Balancer
Nginx, AWS ALB
Distributes requests and routes them to appropriate services
Application Servers
Node.js, Java Spring Boot, Python Flask
Process business logic and handle user requests
Cache
Redis, Memcached
Store frequently accessed data to reduce latency
Database
PostgreSQL, MongoDB
Persist system data reliably
External Services
Third-party APIs
Provide additional features or data not managed internally
Request Flow
1. Client sends request to API Gateway
2. API Gateway routes request to appropriate Application Server
3. Application Server checks Cache for data
4. If data not in Cache, Application Server queries Database
5. Application Server processes data and sends response back through API Gateway
6. API Gateway returns response to Client
7. Application Server may call External Services as needed
Scaling Discussion
Bottlenecks
API Gateway can become a single point of failure
Application Servers may be overwhelmed with requests
Database can become a bottleneck under heavy read/write load
Cache size limits may reduce hit rate
External Services latency can slow down responses
Solutions
Use multiple API Gateway instances with health checks and failover
Scale Application Servers horizontally with auto-scaling
Use database replication and sharding to distribute load
Increase cache size and implement cache eviction policies
Implement asynchronous calls or circuit breakers for External Services
Interview Tips
Time: Spend 10 minutes understanding requirements and clarifying scope, 20 minutes drawing and explaining the architecture, 10 minutes discussing scaling and trade-offs, 5 minutes for questions.
Explain main components clearly and their roles
Describe how data flows through the system
Highlight technology choices and why they fit
Discuss how the design supports scalability and reliability
Mention trade-offs and possible improvements

Practice

(1/5)
1. What does a high level design (HLD) primarily show in a system?
easy
A. The user interface colors and fonts
B. The main components and how they connect
C. The detailed database schema
D. The exact code for each module

Solution

  1. Step 1: Understand the purpose of HLD

    HLD focuses on the big picture, showing main parts and their relationships.

  2. Step 2: Differentiate from detailed design

    Detailed code or UI specifics are not part of HLD but come later in design phases.

  3. Final Answer:

    The main components and how they connect -> Option B

  4. Quick Check:

    HLD = Big parts and connections [OK]
Hint: HLD = big parts + connections, not code or UI [OK]
Common Mistakes:
  • Confusing HLD with detailed design
  • Thinking HLD includes UI styling
  • Assuming HLD shows exact code
2. Which of the following is a correct element to include in a high level design document?
easy
A. Component diagrams showing system parts
B. Detailed API code snippets
C. Exact SQL queries for database
D. Pixel-perfect UI mockups

Solution

  1. Step 1: Identify typical HLD contents

    HLD includes diagrams of components and their interactions, not code or UI details.

  2. Step 2: Eliminate incorrect options

    Code snippets, SQL queries, and UI mockups belong to detailed design or implementation.

  3. Final Answer:

    Component diagrams showing system parts -> Option A

  4. Quick Check:

    HLD = component diagrams [OK]
Hint: HLD shows diagrams, not code or UI details [OK]
Common Mistakes:
  • Including code snippets in HLD
  • Confusing HLD with low-level design
  • Adding UI mockups in HLD
3. Given a high level design showing components A, B, and C connected in sequence, what is the most likely data flow?
medium
A. Data flows from A to B to C
B. Data flows from C to B to A
C. Data flows randomly between components
D. No data flows between components

Solution

  1. Step 1: Analyze component connections

    Sequence connection means data moves in order from first to last component.

  2. Step 2: Determine flow direction

    Data flows from A to B to C as per the sequence shown.

  3. Final Answer:

    Data flows from A to B to C -> Option A

  4. Quick Check:

    Sequence = A -> B -> C data flow [OK]
Hint: Follow arrows in sequence for data flow direction [OK]
Common Mistakes:
  • Reversing data flow direction
  • Assuming random data flow
  • Ignoring component connections
4. A high level design diagram shows a database connected directly to the user interface without any backend service. What is the main issue here?
medium
A. Database should connect only to frontend
B. Too many components included
C. Missing backend layer to handle business logic
D. User interface should connect directly to database

Solution

  1. Step 1: Identify missing architectural layer

    Backend services handle logic and security between UI and database.

  2. Step 2: Understand why direct UI to database is bad

    Direct connection risks security and breaks separation of concerns.

  3. Final Answer:

    Missing backend layer to handle business logic -> Option C

  4. Quick Check:

    Backend needed between UI and database [OK]
Hint: UI never connects directly to database [OK]
Common Mistakes:
  • Thinking UI can safely connect to database
  • Ignoring backend role
  • Confusing component count with design quality
5. When creating a high level design for a scalable web application, which of the following should be included?
hard
A. Detailed SQL queries for data retrieval
B. Exact CSS styles for responsive design
C. User passwords and encryption keys
D. Components like load balancers, web servers, and databases with their interactions

Solution

  1. Step 1: Identify scalable system components

    Load balancers, web servers, and databases are key parts for scalability.

  2. Step 2: Exclude irrelevant details

    CSS styles, SQL queries, and sensitive data are not part of HLD.

  3. Final Answer:

    Components like load balancers, web servers, and databases with their interactions -> Option D

  4. Quick Check:

    HLD = scalable components + interactions [OK]
Hint: Include scalable components, exclude code and secrets [OK]
Common Mistakes:
  • Adding UI styles in HLD
  • Including sensitive data in design
  • Confusing HLD with implementation details
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