Elastic Load Balancer (ELB) in AWS - Complete Guide

1. What is ELB?

AWS Elastic Load Balancer (ELB) is a fully managed service that automatically distributes incoming application traffic across multiple targets (EC2 instances, containers, IP addresses) in one or more Availability Zones (AZs).

2. Key Benefits

✔ High Availability - Automatic failover to healthy targets
✔ Fault Tolerance - Distributes traffic across multiple AZs
✔ Scalability - Handles traffic spikes automatically
✔ Security - Integrated with AWS WAF and Shield
✔ Health Checks - Monitors target health

3. Types of ELB

A. Application Load Balancer (ALB)

• Layer: 7 (HTTP/HTTPS)

• Best For: Web applications, microservices

• Features:

  • Path-based routing (/api, /images)

  • Host-based routing (api.example.com)

  • Supports WebSockets, HTTP/2

  • Integrated with AWS WAF

B. Network Load Balancer (NLB)

• Layer: 4 (TCP/UDP/TLS)

• Best For: Extreme performance, static IPs

• Features:

  • Ultra-low latency (<100ms)

  • Static IP/Elastic IP support

  • Handles millions of requests/sec

  • Preserves source IP

C. Gateway Load Balancer (GWLB)

• Purpose: Deploy 3rd-party virtual appliances

• Protocol: GENEVE (port 6081)

• Use Cases: Firewalls, intrusion detection

D. Classic Load Balancer (CLB)

• Legacy: Avoid for new deployments

• Supports: Both Layer 4 and Layer 7

4. Core Components

5. How ELB Works

Client → Internet → ELB → [Target Group]
                           ├─ EC2 (AZ1)
                           ├─ ECS (AZ2)
                           └─ Lambda

6. Key Features

• Cross-Zone Load Balancing: Even distribution across AZs

• SSL/TLS Termination: Offloads encryption/decryption

• Sticky Sessions: Route requests to same target

• Access Logs: Log all requests to S3

• Integration: Works with Auto Scaling, ECS, Lambda

7. Best Practices

✔ Enable deletion protection for production ELBs
✔ Use ACM for SSL certificates (free)
✔ Configure multi-AZ deployment
✔ Set appropriate idle timeout (ALB: 1-4000 sec)
✔ Monitor HTTPCode_ELB_5XX_Count metric

8. Pricing

• ALB: $0.0225/hour + $0.008/LCU*

• NLB: $0.0225/hour + $0.006/NLCU*

• GWLB: $0.030/hour + $0.005/GLCU*

*LCU = Load Balancer Capacity Unit (based on connections, bandwidth, rule evaluations)

9. Common Use Cases

• Blue/Green Deployments

• A/B Testing

• Multi-tier Applications

• Disaster Recovery

10. Limitations

• ALB: Max 100 rules per listener

• NLB: No HTTP header manipulation

• All ELBs: No built-in caching (use CloudFront)

Would you like a step-by-step setup guide for a specific ELB type? 🚀