Backend Engineering Foundations

A structured visual guide to Backend Engineering, System Design, Distributed Systems, Low Level Design, Databases, and Backend Security.

https://github.com/user-attachments/assets/9f99dac6-4dfe-4012-ab8f-3a70f4baa2d8

Learn backend engineering through structured visual diagrams designed for learning, revision, and interview preparation.

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Purpose

This repository serves as a visual reference for:

• Backend Engineering Fundamentals
• Low Level Design (LLD)
• Object-Oriented Design (OOD)
• SOLID Principles
• Design Patterns
• System Design
• Distributed Systems
• Networking
• Database Internals
• Security Fundamentals
• Scalability & Reliability Patterns
• Technical Interview Preparation

Table of Contents

• Low Level Design (LLD)
• System Design & Backend
• Security
• SQL
• Ongoing Work
• Author

Low Level Design (LLD)

Contents

| No. | Diagram | |:--:|---------| | 1 | Approach to Solving a Design Problem | | 2 | Coupling & Cohesion | | 3 | Object vs Class | | 4 | Four Pillars of OOP | | 5 | Relationships in Object-Oriented Design | | 6 | SOLID Principles Overview | | 7 | Single Responsibility Principle (SRP) | | 8 | Open Closed Principle (OCP) | | 9 | Liskov Substitution Principle (LSP) | | 10 | Interface Segregation Principle (ISP) | | 11 | Dependency Inversion Principle (DIP) | | 12 | Singleton Pattern | | 13 | Factory Pattern | | 14 | Builder Pattern | | 15 | Adapter Pattern | | 16 | Strategy Pattern | | 17 | Observer Pattern | | 18 | Decorator Pattern | | 19 | Facade Pattern |

Approach to Solving a Design Problem

!Approach to Solving a Design Problem

Coupling & Cohesion

!Coupling & Cohesion

Object vs Class

!Object vs Class

Four Pillars of OOP

!Four Pillars of OOP

Relationships in Object-Oriented Design

!Relationships in Object-Oriented Design

SOLID Principles Overview

!SOLID Principles Overview

Single Responsibility Principle (SRP)

!Single Responsibility Principle

Open Closed Principle (OCP)

!Open Closed Principle

Liskov Substitution Principle (LSP)

!Liskov Substitution Principle

Interface Segregation Principle (ISP)

!Interface Segregation Principle

Dependency Inversion Principle (DIP)

!Dependency Inversion Principle

Singleton Pattern

!Singleton Pattern

Factory Pattern

!Factory Pattern

Builder Pattern

!Builder Pattern

Adapter Pattern

!Adapter Pattern

Strategy Pattern

!Strategy Pattern

Observer Pattern

!Observer Pattern

Decorator Pattern

!Decorator Pattern

Facade Pattern

!Facade Pattern

System Design & Backend

Contents

| No. | Diagram | |:--:|---------| | 1 | AWS Frequently Used Services Overview | | 2 | AWS Single Instance Deployment (Basic Overview) | | 3 | Proxy | | 4 | API Gateway & Load Balancer | | 5 | Load Balancer Overview | | 6 | Load Balancer Types (L4, L7, Active-Active, Active-Passive) | | 7 | Load Balancing Algorithms | | 8 | Content Delivery Network (CDN) | | 9 | Caching | | 10 | Rate Limiting | | 11 | Rate Limiting Algorithms | | 12 | Backpressure | | 13 | Queue | | 14 | Retry Mechanism | | 15 | Circuit Breaker Pattern | | 16 | Bulkheads Pattern | | 17 | Failover | | 18 | Failure Handling | | 19 | Graceful Degradation | | 20 | Concurrency vs Parallelism | | 21 | Processes & Threads | | 22 | Consistency Models | | 23 | Consistency in NoSQL | | 24 | PACELC Theorem | | 25 | Consistent Hashing | | 26 | Bloom Filter | | 27 | Merkle Tree | | 28 | Gossip Protocol & Database Failures | | 29 | Leader Election | | 30 | Quorum Algorithm | | 31 | Raft Consensus Algorithm - Part 1 | | 32 | Raft Consensus Algorithm - Part 2 | | 33 | Raft Consensus Algorithm - Part 3 | | 34 | Raft Consensus Algorithm - Part 4 | | 35 | Distributed Lock | | 36 | Federation | | 37 | HTTP Fundamentals - Part 1 | | 38 | HTTP Fundamentals - Part 2 | | 39 | Remote Procedure Call (RPC) | | 40 | Server-Sent Events (SSE) & Webhooks | | 41 | API Versioning | | 42 | Event Driven Architecture | | 43 | Payment Gateway Overview | | 44 | SQL Architecture | | 45 | Write-Ahead Logging & Database Recovery | | 46 | Isolation Levels & Locking | | 47 | Why Backend Shouldn't Serve Static Files |

AWS Frequently Used Services Overview

!AWS Frequently Used Services Overview

AWS Single Instance Deployment (Basic Overview)

!AWS Single Instance Deployment

Proxy

!Proxy

API Gateway & Load Balancer

!API Gateway & Load Balancer

Load Balancer Overview

!Load Balancer Overview

Load Balancer Types (L4, L7, Active-Active, Active-Passive)

!Load Balancer Types

Load Balancing Algorithms

!Load Balancing Algorithms

Content Delivery Network (CDN)

!CDN

Caching

!Caching

Rate Limiting

!Rate Limiting

Rate Limiting Algorithms

!Rate Limiting Algorithms

Backpressure

!Backpressure

Queue

!Queue

Retry Mechanism

!Retry Mechanism

Circuit Breaker Pattern

!Circuit Breaker Pattern

Bulkheads Pattern

!Bulkheads Pattern

Failover

!Failover

Failure Handling

!Failure Handling

Graceful Degradation

!Graceful Degradation

Concurrency vs Parallelism

!Concurrency vs Parallelism

Processes & Threads

!Processes & Threads

Consistency Models

!Consistency Models

Consistency in NoSQL

!Consistency in NoSQL

PACELC Theorem

!PACELC Theorem

Consistent Hashing

!Consistent Hashing

Bloom Filter

!Bloom Filter

Merkle Tree

!Merkle Tree

Gossip Protocol & Database Failures

!Gossip Protocol & Database Failures

Leader Election

!Leader Election

Quorum Algorithm

!Quorum Algorithm

Raft Consensus Algorithm - Part 1

!Raft Consensus Algorithm - Part 1

Raft Consensus Algorithm - Part 2

!Raft Consensus Algorithm - Part 2

Raft Consensus Algorithm - Part 3

!Raft Consensus Algorithm - Part 3

Raft Consensus Algorithm - Part 4

!Raft Consensus Algorithm - Part 4

Distributed Lock

!Distributed Lock

Federation

!Federation

HTTP Fundamentals - Part 1

!HTTP Fundamentals - Part 1

HTTP Fundamentals - Part 2

!HTTP Fundamentals - Part 2

Remote Procedure Call (RPC)

!RPC

Server-Sent Events (SSE) & Webhooks

!SSE & Webhooks

API Versioning

!API Versioning

Event Driven Architecture

!Event Driven Architecture

Payment Gateway Overview

!Payment Gateway Overview

SQL Architecture

!SQL Architecture

Write-Ahead Logging & Database Recovery

!Write-Ahead Logging & Database Recovery

Isolation Levels & Locking

!Isolation Levels & Locking

Why Backend Shouldn't Serve Static Files

!Why Backend Shouldn't Serve Static Files

Security

Contents

| No. | Diagram | |:--:|---------| | 1 | Authentication vs Authorization | | 2 | Cookies, Sessions & Replay Attacks | | 3 | Browser Security | | 4 | Privilege Escalation, CSRF, XSS & Injection Attacks |

Authentication vs Authorization

!Authentication vs Authorization

Cookies, Sessions & Replay Attacks

!Cookies, Sessions & Replay Attacks

Browser Security

!Browser Security

Privilege Escalation, CSRF, XSS & Injection Attacks

!Privilege Escalation, CSRF, XSS & Injection Attacks

SQL

Contents

| No. | Diagram | |:--:|---------| | 1 | Subqueries | | 2 | CTEs & Views | | 3 | SQL Comparison - Subquery vs CTE vs Temp Table vs CTAS vs Views | | 4 | Window Functions | | 5 | Regular Expressions | | 6 | Database Indexing | | 7 | Clustered vs Non-Clustered Indexes |

Subqueries

!Subqueries

CTEs & Views

!CTEs & Views

SQL Comparison - Subquery vs CTE vs Temp Table vs CTAS vs Views

!SQL Comparison

Window Functions

!Window Functions

Regular Expressions

!Regular Expressions

Database Indexing

!Database Indexing

Clustered vs Non-Clustered Indexes

!Clustered vs Non-Clustered Indexes

Ongoing Work

New concepts, diagrams, and improvements are added regularly as the repository evolves. If this repository adds value to your learning journey, a ⭐ is always appreciated.

Author

Built and maintained by Nikhil Gupta.