What high level design encompasses in HLD - System Design Guide

Problem Statement

When building complex software, teams often struggle with unclear system boundaries and component responsibilities. This leads to confusion, duplicated work, and integration failures as the project grows.

Solution

High level design breaks down the system into major components and defines their interactions clearly. It provides a blueprint showing how data flows and how parts communicate, helping teams understand the overall structure before detailed coding begins.

Architecture

Client UI

→API Gateway

↓

Database

This diagram shows a high level design with client UI, API gateway, service layer, database, and cache components and their data flow.

Trade-offs

✓ Pros

→

Clarifies system structure and component responsibilities early.

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Facilitates communication among team members and stakeholders.

→

Helps identify integration points and potential bottlenecks.

→

Supports scalability planning by showing component interactions.

✗ Cons

→

May oversimplify details leading to missed edge cases.

→

Requires updates as system evolves, or it becomes outdated.

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Can delay coding if teams spend too much time perfecting the design.

Use high level design when starting medium to large projects with multiple components or teams, especially when integration complexity is expected.

Avoid detailed high level design for very small or prototype projects where speed is more important than structure.

Real World Examples

Amazon

Amazon uses high level design to define service boundaries in their microservices architecture, ensuring clear API contracts and data flow between services.

Netflix

Netflix creates high level designs to map out their content delivery network and streaming services, coordinating components like user interface, recommendation engine, and data storage.

Uber

Uber applies high level design to separate rider, driver, and payment services, enabling independent scaling and development.

Alternatives

Low Level Design (LLD)

Focuses on detailed internal logic, data structures, and algorithms within components rather than overall system structure.

Use when: Choose LLD when component interfaces are defined and detailed implementation plans are needed.

Prototyping

Builds quick, simplified versions of the system to explore ideas rather than defining full architecture upfront.

Use when: Choose prototyping when requirements are unclear or rapid feedback is needed.

Summary

High level design defines the main components and their interactions in a system.

It helps teams understand the overall structure before detailed coding begins.

This design approach improves communication and planning for complex projects.

Practice

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