Elastic Load Balancing & Auto Scaling in AWS

Mastering Scalability, High Availability, and Fault Tolerance

In this chapter, we’ll take a deep dive into two essential AWS services—Elastic Load Balancing (ELB) and Auto Scaling—which are foundational for building scalable, reliable, and resilient cloud applications.

Part 1: Elastic Load Balancing (ELB)

What is Elastic Load Balancing?

Elastic Load Balancing (ELB) automatically distributes incoming application traffic across multiple targets (EC2, containers, Lambda) in one or more Availability Zones, ensuring high availability, fault tolerance, and performance.

It acts as the “traffic cop” in your cloud architecture, ensuring no single server bears too much load.

Types of Load Balancers

AWS provides three main types of ELBs. Each is tailored to different types of applications:

⚙️ Key Features of ELB

• Health Checks: Automatically routes traffic only to healthy targets.
• SSL Termination: Offload SSL processing at the load balancer.
• Sticky Sessions: Maintain user sessions with a specific backend.
• Path-Based Routing: Route /api to one service and /static to another (ALB).
• WebSocket Support: ALB supports WebSocket protocols for real-time apps.
• IPv6 Support, WAF Integration, and Cross-Zone Load Balancing.

🛠️ How to Create an Application Load Balancer (ALB)

Using AWS Console:

1. Open EC2 → Load Balancers → Create Load Balancer → Select ALB
2. Define name, scheme (internet-facing), and VPC/subnets
3. Choose Security Groups
4. Add Listeners (e.g., HTTP/HTTPS)
5. Configure Target Groups:
   • Target Type: Instance, IP, Lambda
   • Health checks path: /health or /
6. Register Targets (EC2s)
7. Review and Create

Using AWS CLI:

aws elbv2 create-load-balancer \
  --name my-alb \
  --subnets subnet-aaa subnet-bbb \
  --security-groups sg-12345678 \
  --scheme internet-facing \
  --type application

aws elbv2 create-load-balancer \
  --name my-alb \
  --subnets subnet-aaa subnet-bbb \
  --security-groups sg-12345678 \
  --scheme internet-facing \
  --type application

Real Use Case Scenarios for ELB

Best Practices for ELB

• Enable Access Logs for monitoring and audit.
• Use SSL/TLS termination to offload decryption from backend servers.
• Always deploy across multiple AZs for high availability.
• Protect with AWS WAF for web attack mitigation.
• Use ALB with ECS/EKS for containerized environments.

Part 2: Auto Scaling (ASG)

🔄 What is Auto Scaling?

Auto Scaling allows AWS to automatically add (scale out) or remove (scale in) compute resources (like EC2 instances) based on real-time demand, saving costs while ensuring consistent performance.

Auto Scaling involves:

• Auto Scaling Group (ASG)
• Launch Template or Launch Configuration
• Scaling Policies

Key Components of Auto Scaling

How to Configure an Auto Scaling Group

Step-by-Step (AWS Console):

1. Go to EC2 → Auto Scaling Groups → Create ASG
2. Choose or create a Launch Template
3. Set Group Name, VPC, and Subnets
4. Choose Load Balancer (optional but recommended)
5. Set:
   • Desired Capacity (e.g., 2)
   • Minimum Instances (e.g., 1)
   • Maximum Instances (e.g., 5)
6. Add Scaling Policies:
   • Target Tracking (e.g., maintain CPU at 60%)
   • Step Scaling (scale by count or percentage)
   • Scheduled Scaling (e.g., increase at 9 AM)

Example CLI for Auto Scaling

✅ Create Launch Template:

aws ec2 create-launch-template \
  --launch-template-name my-template \
  --version-description "v1" \
  --launch-template-data file://template-data.json

aws ec2 create-launch-template \
  --launch-template-name my-template \
  --version-description "v1" \
  --launch-template-data file://template-data.json

✅ Create Auto Scaling Group:

aws autoscaling create-auto-scaling-group \
  --auto-scaling-group-name my-asg \
  --launch-template "LaunchTemplateName=my-template,Version=1" \
  --min-size 1 --max-size 5 --desired-capacity 2 \
  --vpc-zone-identifier "subnet-aaa,subnet-bbb"

aws autoscaling create-auto-scaling-group \
  --auto-scaling-group-name my-asg \
  --launch-template "LaunchTemplateName=my-template,Version=1" \
  --min-size 1 --max-size 5 --desired-capacity 2 \
  --vpc-zone-identifier "subnet-aaa,subnet-bbb"

Real-World Examples of Auto Scaling

🔒 Security Considerations for ELB & ASG

• Place EC2s in private subnets, only ALB in public
• Use IAM roles for EC2s for minimal access
• Configure Security Groups: ELB → EC2s only on required ports
• Regularly rotate AMIs and patch instances
• Use Auto Recovery feature for failed instances

Monitoring & Logging

Use CloudWatch Alarms to trigger scale-out or scale-in policies.

🔄 ELB + ASG Architecture Diagram (Textual)

User
 ↓
[Route 53 - DNS]
 ↓
[Application Load Balancer]
 ↓
[Auto Scaling Group]
 ↳ EC2 Instance 1
 ↳ EC2 Instance 2
 ↳ EC2 Instance (scaled dynamically)
 ↓
[Database - RDS/DynamoDB]

User
 ↓
[Route 53 - DNS]
 ↓
[Application Load Balancer]
 ↓
[Auto Scaling Group]
 ↳ EC2 Instance 1
 ↳ EC2 Instance 2
 ↳ EC2 Instance (scaled dynamically)
 ↓
[Database - RDS/DynamoDB]

✅ This pattern ensures resilience, cost optimization, and scalability.

Summary