15. Load Balancers

Load Balancers

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Prerequisites

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1. Load Balancers

Load Balancer is a core component of modern cloud architecture. It provides Traffic distribution across multiple servers

A Load Balancer is:

• An entry point for user requests
• A service that distributes traffic to multiple targets

👉 Instead of:

User → EC2 (single server)

👉 You use:

User → Load Balancer → Multiple EC2

Load Balancer → Target Group ← Auto Scaling Group

Without Load Balancer:

• Single point of failure
• Cannot scale easily
• Uneven traffic distribution

With Load Balancer:

• High availability
• Scalability
• Fault tolerance

User → Load Balancer → Target Group → EC2

Load Balancer does NOT directly manage EC2. It uses Target Groups

• Removes unhealthy instances

  1-1. Health Check

Load Balancer uses Target Group health checks:

• Healthy → receive traffic
• Unhealthy → excluded

GET /health

1-2. Concept

✔️ Decoupling

• Load Balancer separates users from backend services
• Backend instances can be replaced without affecting clients

✔️ Scalability

• Works with Auto Scaling Group (ASG)
• Automatically distributes traffic as instances scale in/out

✔️ Fault Tolerance

• Detects unhealthy instances using health checks
• Routes traffic only to healthy targets
• Prevents service disruption when instances fail

2. Types of Load Balancer

2-1. ALB (Application Load Balancer)

• Layer 7 (HTTP/HTTPS)
• Path-based routing
• Host-based routing

/api → Service A
/web → Service B

2-2. NLB (Network Load Balancer)

• Layer 4 (TCP/UDP)
• High performance
• Low latency

2-3. GWLB (Gateway Load Balancer)

• Layer 3 / Layer 4
• Used for network security appliances
• Transparent traffic inspection
• Uses GENEVE protocol (port 6081)

👉 Example:

Client → GWLB → Firewall (EC2) → GWLB → Destination

👉 Use cases:

• Firewall
• Intrusion Detection System (IDS)
• Deep Packet Inspection

2-4. CLB (Classic Load Balancer)

• Legacy (not recommended)
• Limited features compared to ALB/NLB

3. How to create Target Groups

3-1. Search EC2

3-2. Click Navigation pane → “Load Balancers”

3-3. Click Button → “Create load balancer”

3-4. Step 1. Select Load balancer types

3-5. Step 2. Basic Configuration

3-6. Step 3. Network mapping

3-7. Step 4. Set Listner

3-8. Check Security and In/Outbound rules

4. OPTIONAL

4-1. Edit Listner

5. Related Concepts

• Components
  • Target Groups
  • Auto Scaling Groups