System Design Basics

Table of Contents

Table of Contents ............................................................................................................................ 2

1. Why Should You Learn System Design? ..................................................................................... 4

It Matters at Every Stage of Your Career ...................................................................................... 4

Real-World Moments That Make You Think About System Design .............................................. 4

2. What is System Design? .............................................................................................................. 5

2.1 Low-Level Design (LLD) ......................................................................................................... 5

2.2 High-Level Design (HLD) ........................................................................................................ 5

3. Why Do We Need Distributed Systems? ...................................................................................... 5

Limitations of a Single Machine .................................................................................................... 5

What Distributed Systems Solve .................................................................................................. 6

4. Vertical Scaling vs Horizontal Scaling .......................................................................................... 6

4.1 Vertical Scaling (Scale Up) ..................................................................................................... 6

4.2 Horizontal Scaling (Scale Out) ................................................................................................ 6

4.3 Comparison: Vertical vs Horizontal Scaling ............................................................................ 7

5. Real-Life Story: How a Website Scales ........................................................................................ 8

The Del.icio.us Story (2003) ......................................................................................................... 8

The Problem Del.icio.us Solved ................................................................................................ 8

The Core Functionality — Simplified ......................................................................................... 8

6. DNS: How Browsers Find Your Server ......................................................................................... 8

The Core Problem ........................................................................................................................ 8

Step 1 — Buying a Domain Name ................................................................................................ 8

Step 2 — Linking Domain to Your Server (A Record) ................................................................... 8

Step 3 — DNS Servers: The Distributed Directory ........................................................................ 9

7. Handling Traffic & Deployments — Load Balancer Introduction ................................................... 9

The Single Server Bottleneck ....................................................................................................... 9

Problem A — Deployment Downtime ........................................................................................ 9

Problem B — Traffic Spikes & Server Crashes ......................................................................... 9

The Solution: Adding Multiple Servers .......................................................................................... 9

8. Running Out of Storage — Sharding .......................................................................................... 10

The Storage Crisis ...................................................................................................................... 10

Choosing the Sharding Key ........................................................................................................ 10

Shard Mapping Algorithms ......................................................................................................... 10

Approach 1: Modulo Hashing (userId % number_of_shards) .................................................. 10

Approach 2: Range-Based Sharding ....................................................................................... 11

9. Consistent Hashing .................................................................................................................... 11

How It Works — Step by Step .................................................................................................... 11

Implementation Details ............................................................................................................... 12

📸 @codenexuswithashish Page 2 LinkedIn · TopmateSystem Design Notes · Distributed Systems & Load Balancing

The Problem with Basic Consistent Hashing .............................................................................. 12

The Fix: Virtual Nodes (Vnodes) ................................................................................................. 13

10. Deep Dive: Load Balancer ....................................................................................................... 13

10.1 What is a Load Balancer? ................................................................................................... 13

10.2 Core Concept & Architecture .............................................................................................. 13

10.3 Benefits: Scalability (Zero-Downtime Deployments) ........................................................... 14

10.4 Benefits: Resilience & High Availability ............................................................................... 14

Auto-Scaling (Dynamic Capacity) ............................................................................................ 14

Health Checks (Automatic Failure Detection) .......................................................................... 15

10.5 Benefits: Security (DDoS Protection) .................................................................................. 15

10.6 Benefits: Performance (SSL Offloading & Compression) .................................................... 15

SSL/TLS Termination .............................................................................................................. 15

Traffic Compression ................................................................................................................ 15

10.7 How a Load Balancer Works: The Reverse Proxy .............................................................. 16

Security Benefit of Reverse Proxy ........................................................................................... 16

10.8 Health Checks .................................................................................................................... 16

Example AWS Health Check Configuration ............................................................................ 16

10.9 How Load Balancers Scale Themselves ............................................................................. 17

10.10 Load Balancing Algorithms ............................................................................................... 17

Algorithm 1: Round Robin (Most Common) ............................................................................. 17

Algorithm 2: Weighted Round Robin ....................................................................................... 17

Algorithm 3: IP Hash ............................................................................................................... 17

10.11 Types of Load Balancers .................................................................................................. 17

11. Further Reading & Questions to Explore .................................................................................. 18

Question 1: Global Server Load Balancing (GSLB) .................................................................... 18

Question 2: Session Stickiness .................................................................................................. 18

Question 3: Static vs Dynamic Content ...................................................................................... 18

12. References & Learning Resources........................................................................................... 18

YouTube Channels ..................................................................................................................... 18

Websites & Documentation ........................................................................................................ 18

Diagramming Tool ...................................................................................................................... 19

13. Guideline for Future Notes ....................................................................................................... 19

What High-Level Design (HLD) Notes Will Cover ....................................................................... 19

What HLD Notes Will NOT Cover ............................................................................................... 19