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System Design Basics

Table of Contents​

What is System Design?​

System Design is a process where you plan, define, and design systems for specific functional and non-functional requirements. Main focus is making the system scalable, reliable, efficient and maintainable.

Simple Analogy​

Think of designing a building:

  • Small building (single user app) → just need a basic plan
  • Skyscraper (large scale systems like Netflix, Amazon) → need to consider structural integrity, elevators, emergency exits, and traffic flow

Key Goals​

  1. Scalability: System can handle lots of users and data

    • Example: Amazon system stays up during Black Friday sales

  2. Reliability: System never fails, if it fails it recovers quickly

    • Example: If payment app server fails, another server takes responsibility

  3. Performance: Fast response and high throughput

    • Example: Instagram image uploads are visible to other users immediately

  4. Maintainability: Easy to modify, rollback and update

    • Example: Adding new features doesn't impact the existing system

  5. Cost Effectiveness: Efficient use of resources to keep system affordable

    • Example: Using servers efficiently reduces energy costs

Why is it Important?​

  1. Real World Challenges: Large scale systems are complex. Good design keeps systems running smoothly

    • Example: Netflix provides seamless streaming for millions of users

  2. High Availability Systems: Systems that run 24/7

    • Example: Banking systems can't afford downtime

  3. Better User Experience: Better system performance = more users. If it's slow, users leave

  4. Future Growth: Scalability and maintainability are crucial for expanding your system

  5. Interview Prep: Critical and important part of technical interviews

High Level Design vs Low Level Design​

There are 2 important aspects in System Design:

  • High Level Design (HLD)
  • Low Level Design (LLD)

High Level Design (HLD)​

Focus on big picture of the system. We take care of overall architecture and main components.

Key Features:

  • Architecture Overview
  • Tech Stack selection
  • Component interaction
  • Scalability and Reliability
  • Load Distribution

Example: Video Streaming Platform (Netflix, Prime Video)

Components:

  • Frontend: Compatible on web and mobile
  • Backend Services: User authentication, subscriptions, video list, recommendation engine
  • Database: Storing video metadata (NoSQL)
  • Content Delivery Network (CDN): Deliver videos everywhere
  • Caching: Storing data in memory for frequent access (Redis)

Flow: User request on frontend → Load balancer forwards request to backend → Backend fetches data → Video streams via CDN

When to use HLD:

  • When creating new system design and you want to understand overall architecture
  • When you need to explain to non-technical stakeholders

Low Level Design (LLD)​

LLD focuses on internal details of system. It defines class diagrams, algorithms, and detailed logic.

Key Features:

  • Class Diagrams: Classes, methods, objects, properties, and relationships between them
  • Database Schema: Tables and relationships detailed structure
  • Detailed Logic: Functions and algorithm implementations
  • Design Patterns: Use of Object Oriented Design principles like SOLID, YAGNI, KISS, DRY

Example: Video Streaming Platform (Detailed)

Class Design:

  • User: UserID, name, subscription plan, watch history
  • Video: VideoID, title, genre, ratings, CDN URL
  • RecommendationEngine: generateRecommendations(userID) method

Database Schema:

  • User table: userID, name, subscriptionType
  • Video table: videoID, title, genre, cdnUrl

Algorithm:

  • Collaborative filtering algorithm for Recommendation Engine

When to use LLD:

  • When you need to implement system in detail
  • When you discuss implementation details with dev team