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🛠️ Step-by-Step: Create and Use Application Load Balancer

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🔹 Step 1: Launch EC2 Instances

Launch 2 EC2 instances (Amazon Linux 2):

1. AMI: Amazon Linux 2

2. Instance Type: t2.micro

3. User Data (to install Apache):

bashCopyEdit#!/bin/bash
yum update -y
yum install -y httpd
echo "Hello from EC2-1" > /var/www/html/index.html
systemctl start httpd
systemctl enable httpd

For 2nd instance, change content to: "Hello from EC2-2"

4. Security Group (for EC2):

   • Inbound Rule: HTTP (80) from 0.0.0.0/0

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🔹 Step 2: Create a Target Group

1. Open EC2 Console → Target Groups → Create Target Group

2. Target Type: Instance

3. Protocol: HTTP, Port: 80

4. VPC: Select the one where EC2 is running

5. Name: web-tg

6. Health Check Path: /index.html

7. Register both EC2s

8. Click Create

📌 Now your target group is ready and will monitor instance health.

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🔹 Step 3: Create the Application Load Balancer (ALB)

1. EC2 Console → Load Balancers → Create Load Balancer → Choose Application Load Balancer

2. Name: my-alb

3. Scheme: Internet-facing

4. IP type: IPv4

5. Listeners:

   • Protocol: HTTP

   • Port: 80

6. Availability Zones:

   • Choose at least 2 subnets in different AZs where your EC2s exist

7. Security Group for ALB:

   • Allow HTTP (80) from 0.0.0.0/0

8. Routing:

   • Target group: web-tg

   • Listener rule: forward all requests to this group

9. Click Create Load Balancer

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🔹 Step 4: Test Your ALB

1. Go to EC2 → Load Balancers → Select my-alb

2. Copy DNS Name (e.g., my-alb-123456789.ap-south-1.elb.amazonaws.com)

3. Open in browser → refresh multiple times

✅ You’ll see:

• “Hello from EC2-1”

• “Hello from EC2-2”
  (as traffic alternates between targets)

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⚙️ How ALB Works (Internally)

1. User makes HTTP request to ALB DNS.

2. ALB checks Listener Rules (port 80, HTTP).

3. Routes request to associated Target Group.

4. Health check ensures traffic is only sent to healthy EC2s.

5. Target EC2 receives traffic, processes it, and responds.

6. ALB forwards the response back to the client.

🔧 Optimization Tips for ALB

✅ 1. Enable HTTP → HTTPS Redirection

• Add HTTPS listener (port 443).

• Create a certificate using AWS ACM.

• Redirect HTTP to HTTPS in listener rules.

✅ 2. Path-Based Routing (Microservices)

• Use multiple Target Groups:

  • /api/* → backend EC2 or ECS service

  • /web/* → frontend EC2

• Helps isolate services and scale independently

✅ 3. Enable Access Logs

• Store logs in an S3 bucket

• Helps in debugging and analyzing traffic

✅ 4. Enable Sticky Sessions (Session Affinity)

• Go to Target Group → Attributes

• Enable stickiness using cookies (useful for stateful apps)

✅ 5. Auto Scaling Integration

• Attach Target Group to an Auto Scaling Group

• Automatically adds/removes EC2 instances based on traffic load

✅ 6. CloudWatch Alarms

• Monitor:

  • HealthyHostCount

  • TargetResponseTime

  • HTTPCode_ELB_5XX_Count

Set alarms and notifications for failures.

✅ 7. Use WAF with ALB

• Protect from common threats (SQLi, XSS)

• Create a Web ACL and associate it with your ALB

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🔁 Recap Summary

—> In next part we will setup a ALB