Day 46 — Elastic Load Balancers (ELB) in AWS

Today I dove into Elastic Load Balancing (ELB) — a critical service in AWS that ensures high availability, scalability, and reliability of applications by distributing traffic across multiple targets (like EC2, containers, or IPs).

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🔁 What is Load Balancing?

When deploying applications on clusters of servers, you don't want users to interact with servers directly. Instead, you provide a single endpoint, and behind the scenes a Load Balancer routes the incoming traffic to the appropriate backend servers.

🚪 Load Balancer Ports:

• Frontend Port (Listener): Listens for incoming user requests

  • Examples: 80 (HTTP), 443 (HTTPS), 25 (SMTP)

• Backend Port: Where your app/service is running on EC2/container

  • Examples: 80, 443, 8080, etc.

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⚙️ What is Elastic Load Balancer (ELB)?

Elastic Load Balancing (ELB) automatically distributes incoming application or network traffic across multiple targets, including:

• EC2 instances

• ECS containers

• IP addresses

• Lambda (for ALB only)

It works across multiple Availability Zones to improve fault tolerance and high availability.

🔗 Learn more: https://aws.amazon.com/elasticloadbalancing/

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🧱 Types of Load Balancers in AWS

1. 🌀 Classic Load Balancer (CLB)

• Legacy load balancer

• Operates at Layer 4 (TCP) or Layer 7 (HTTP)

• Best for simple load balancing across EC2

• Limited features compared to ALB/NLB

2. 🧠 Application Load Balancer (ALB)

• Operates at Layer 7 (HTTP/HTTPS)

• Smart routing based on:

  • Path-based routing (e.g., /images, /api)

  • Host-based routing (e.g., api.example.com)

  • Header/cookie inspection

• Supports WebSockets and serverless (Lambda) targets

• Ideal for microservices and modern web apps

3. ⚡ Network Load Balancer (NLB)

• Operates at Layer 4 (TCP/UDP)

• Handles millions of requests per second

• Ultra-low latency, static IP, and TLS termination

• Great for performance-critical, gaming, or VoIP apps

4. 🚪 Gateway Load Balancer (GWLB) (for advanced use cases)

• Helps with third-party virtual appliances (e.g., firewalls, intrusion detection)

• Not commonly used in beginner setups

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✅ ELB Benefits

• High Availability: Works across AZs

• Scalability: Automatically adapts to incoming traffic

• Resilience: Replaces unhealthy targets automatically

• Central Endpoint: Simple DNS for app access

• Secure: Works with SSL/TLS and integrates with IAM/ACM

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🧠 What I Learned Today

• ELB is essential to scale and secure distributed applications

• Choosing the right load balancer depends on the protocol, routing needs, and performance requirements

• ALB is ideal for modern apps, while NLB is best for high-speed network-level needs

Next: I’ll explore Amazon CloudWatch

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