KISS (Keep It Simple) in LLD - Architecture Diagram

System Overview - KISS (Keep It Simple)

The KISS principle means designing systems in the simplest way possible. It avoids unnecessary complexity to make systems easier to build, understand, and maintain. Simple designs reduce bugs and improve scalability.

Architecture Diagram

User
  |
Load Balancer
  |
API Service
  |
Cache
  |
Database

Components

User

user

Initiates requests to the system

Load Balancer

load_balancer

Distributes incoming requests evenly to API services

API Service

service

Handles business logic simply without extra layers

Cache

cache

Speeds up data access by storing frequently used data

Database

database

Stores persistent data in a straightforward manner

Request Flow - 9 Hops

User → Load Balancer

Load Balancer → API Service

API Service → Cache

Cache → API Service

API Service → Database

Database → API Service

API Service → Cache

API Service → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Cache

Impact:Cache misses increase, causing more database queries and higher latency

Mitigation:System continues working by querying the database directly; cache rebuilds over time

Architecture Quiz - 3 Questions

Why does the system use a cache before querying the database?

A To store user credentials

B To reduce database load and speed up responses

C To replace the database entirely

D To balance load between servers

Design Principle

This system shows the KISS principle by using a straightforward architecture with minimal components. Each part has a clear, simple role, avoiding unnecessary complexity. This makes the system easier to understand, maintain, and scale.

Practice

1. What is the main goal of the KISS principle in system design?

easy

A. To add as many features as possible

B. To keep designs simple and easy to understand

C. To use complex algorithms for better performance

D. To focus only on the user interface

Solution

1. Step 1: Understand the KISS principle meaning

   KISS stands for "Keep It Simple, Stupid" and encourages simplicity in design.

2. Step 2: Identify the goal of simplicity

   The goal is to make systems easier to build, test, and maintain by avoiding unnecessary complexity.

3. Final Answer:

   To keep designs simple and easy to understand -> Option B

4. Quick Check:

   KISS = Keep It Simple [OK]

Hint: KISS means simple and clear design only [OK]

Common Mistakes:

• Thinking KISS means adding more features
• Confusing simplicity with lack of functionality
• Assuming KISS ignores performance

2. Which of the following is the best example of applying KISS in system design?

easy

A. Implementing a custom encryption algorithm instead of a standard one

B. Adding multiple layers of caching without clear need

C. Using a single, clear API endpoint instead of multiple complex ones

D. Designing a UI with many animations and effects

Solution

1. Step 1: Identify simple design choices

   A single clear API endpoint reduces complexity and is easier to maintain.

2. Step 2: Compare other options

   Adding unnecessary caching layers, custom encryption, or flashy UI adds complexity without clear benefit.

3. Final Answer:

   Using a single, clear API endpoint instead of multiple complex ones -> Option C

4. Quick Check:

   Simplicity means fewer, clearer components [OK]

Hint: Choose the simplest clear solution [OK]

Common Mistakes:

• Believing more features always mean better design
• Ignoring maintainability for flashy effects
• Over-engineering solutions

3. Consider this simple system design: a service receives requests and stores data in a database. Which design follows KISS best?

medium

A. Service directly writes to one database without extra layers

B. Service writes to multiple databases with complex syncing logic

C. Service uses multiple caches and queues before writing

D. Service encrypts data multiple times before storing

Solution

1. Step 1: Analyze the simplest design

   Directly writing to one database is straightforward and easy to maintain.

2. Step 2: Evaluate complexity of other options

   Multiple databases, caches, queues, or repeated encryption add complexity and potential failure points.

3. Final Answer:

   Service directly writes to one database without extra layers -> Option A

4. Quick Check:

   Simple direct design = KISS [OK]

Hint: Pick the design with least moving parts [OK]

Common Mistakes:

• Assuming more layers improve reliability always
• Ignoring maintenance overhead of complex syncing
• Overcomplicating encryption unnecessarily

4. You have a system with multiple unnecessary components causing delays. Which change best applies KISS to fix it?

medium

A. Add more logging to track delays

B. Add retries and timeouts to every component

C. Increase hardware resources without changing design

D. Remove extra components and keep only essential parts

Solution

1. Step 1: Identify unnecessary complexity

   Extra components cause delays and complexity, violating KISS.

2. Step 2: Simplify by removing non-essential parts

   Removing unnecessary parts reduces complexity and improves performance.

3. Final Answer:

   Remove extra components and keep only essential parts -> Option D

4. Quick Check:

   Simplify by cutting non-essential parts [OK]

Hint: Cut what is not needed to simplify [OK]

Common Mistakes:

• Adding more features instead of simplifying
• Ignoring root cause of delays
• Relying only on hardware upgrades

5. You must design a notification system that sends alerts to users. Which approach best follows KISS while ensuring scalability?

hard

A. Use a simple queue to process notifications one by one with retry logic

B. Build a complex microservices architecture with multiple databases and caches

C. Send notifications directly from the main application without queueing

D. Implement a custom protocol for notifications with encryption and compression

Solution

1. Step 1: Identify simple scalable design

   A queue with retry logic is simple and can handle load by processing messages sequentially.

2. Step 2: Compare complexity and scalability

   Complex microservices add overhead; direct sending risks overload; custom protocol adds unnecessary complexity.

3. Final Answer:

   Use a simple queue to process notifications one by one with retry logic -> Option A

4. Quick Check:

   Simple queue = scalable and clear [OK]

Hint: Simple queue with retry scales well [OK]

Common Mistakes:

• Over-engineering with microservices too early
• Ignoring retry and failure handling
• Skipping queueing causing overload