🔁 Load Balancer

📌 Purpose:

Ensures performance, availability, fault tolerance, and scalability by distributing traffic across servers.

🛠 Examples:

• AWS ELB
• Google Cloud Load Balancing
• HAProxy (Layer 4/7)

⭐ Key Features:

• Traffic Distribution:

  • Round Robin
  • Least Connections
  • Weighted Distribution

• Health Checks: Detects and removes unhealthy servers

• Session Persistence (Sticky Sessions): IP-based or Cookie-based

• SSL Termination: Handles HTTPS at entry point

• High Availability & Failover

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🧱 Types:

1. Layer 4 Load Balancer (Transport Layer)

   • Uses IP addresses, TCP/UDP ports
   • Fast, low-level routing

2. Layer 7 Load Balancer (Application Layer)

   • Advanced routing using:

     • HTTP Methods
     • URLs, Query Strings
     • Headers, Cookies
     • Application logic (e.g., /api, /images)

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🔄 Reverse Proxy

📌 Features:

• Security & Abstraction: Hides backend servers (IP, port)
• Centralized SSL Termination
• Caching: Static & dynamic content
• Compression: Improves performance
• Load Balancing Capabilities
• URL Rewriting & Routing

✅ Use Case:

Sits in front of backend servers and forwards requests.

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🧠 Difference Between Reverse Proxy & Load Balancer:

• Reverse Proxy = Receptionist: receives requests and passes them inside
• Load Balancer = Smart receptionist: chooses the best backend to avoid overload

✅ A load balancer is a specialized type of reverse proxy

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🌐 Nginx

📌 Type:

Multi-purpose web server and reverse proxy

🔧 Can Do:

• Serve static files (HTML, CSS, JS, images)
• Reverse proxy to backend servers
• Load balancing (basic)
• SSL termination
• HTTP caching & compression

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⚡ HAProxy

📌 Type:

Specialized load balancer for high-performance use

🔧 Can Do:

• Load balancing (L4 + L7)
• Handle millions of requests/sec
• Server health checks
• SSL termination (with config)
• Advanced TCP/HTTP routing

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🆚 Nginx vs HAProxy

Use Case	Best Tool
Static file serving	✅ Nginx
Web server with reverse proxy	✅ Nginx
Simple app hosting + load balancing	✅ Nginx
High-speed traffic distribution	✅ HAProxy
Advanced TCP load balancing (L4)	✅ HAProxy

Tool	Analogy
Nginx	Swiss Army knife – does many things (web server, proxy, SSL, load balancer)
HAProxy	Formula 1 car – does one thing (load balancing) extremely well

➡️ Typical Setup: Internet → Nginx (reverse proxy, SSL) → HAProxy (load balancer) → App Servers

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🚪 API Gateway

📌 Purpose:

Central entry point in microservices architectures.

🛠 Examples:

• Amazon API Gateway
• Apigee (Google)
• Kong Gateway
• Netflix Zuul

⭐ Features:

• Single Point of Entry
• Request Routing
• Authentication & Authorization
• Rate Limiting & Throttling
• Request/Response Transformation
• API Aggregation
• Caching
• Logging & Monitoring
• Protocol Translation

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🧭 When to Use What?

Goal	Use
High availability & traffic distribution	✅ Load Balancer
Security, caching, flexible routing	✅ Reverse Proxy
Managing APIs/microservices	✅ API Gateway

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