KISS (Keep It Simple) in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why is simplicity important in system design?

Consider a system designed with many complex components and dependencies. What is the main benefit of keeping the design simple?

A It reduces the chance of bugs and makes the system easier to maintain.

B It allows the system to use the most advanced technologies regardless of complexity.

C It makes the system design look more impressive to stakeholders.

D It ensures the system has the maximum number of features from the start.

💡 Hint

Think about how complexity affects maintenance and errors.

Simplicity helps reduce bugs and makes it easier to understand and maintain the system over time.

❓ Architecture

intermediate

Choosing between a simple and complex architecture

You need to design a user authentication system. Which design follows the KISS principle best?

A Implement a complex multi-layered security system with many encryption steps and fallback mechanisms.

B Build a system that integrates multiple third-party authentication providers with custom adapters for each.

C Create separate microservices for login, logout, session, token refresh, and user profile management from the start.

D Use a single service that handles login, logout, and session management with clear, simple APIs.

💡 Hint

Focus on simplicity and avoiding unnecessary complexity early on.

A single service with clear APIs is simpler to build and maintain, following KISS.

❓ scaling

advanced

Scaling a simple design without breaking KISS

You have a simple web service that handles 100 requests per second. Traffic is expected to grow to 10,000 requests per second. Which approach best scales the system while keeping it simple?

A Add a load balancer and replicate the existing service instances horizontally without changing the core logic.

B Rewrite the service using multiple complex caching layers and distributed databases immediately.

C Split the service into many microservices handling small parts of the logic before traffic increases.

D Add a message queue and asynchronous processing for all requests regardless of current load.

💡 Hint

Think about scaling by adding more of the same simple components first.

Horizontal scaling with load balancers keeps the design simple and effective for growth.

❓ tradeoff

advanced

Tradeoff between simplicity and feature richness

You are designing a messaging app. Adding end-to-end encryption increases complexity. What is a good KISS-based approach?

A Skip encryption entirely to keep the system as simple as possible forever.

B Add end-to-end encryption from the start to avoid redesigning later, even if it complicates the initial design.

C Start with a simple messaging system without encryption, then add encryption later once the core works well.

D Build two separate apps: one simple without encryption and one complex with encryption.

💡 Hint

Consider starting simple and adding complexity only when needed.

Starting simple and adding features later follows KISS and reduces initial complexity.

❓ estimation

expert

Estimating system complexity impact on maintenance effort

A simple system has 5 components and requires 10 hours of maintenance per month. A complex system has 15 components with many dependencies. Assuming maintenance effort grows quadratically with component count, estimate the monthly maintenance hours for the complex system.

A 30 hours

B 90 hours

C 45 hours

D 150 hours

💡 Hint

Use the formula: effort ∝ (number of components)^2.

Simple system: 5 components → 10 hours. Complex system: 15 components → (15/5)^2 * 10 = 9 * 10 = 90 hours.