🌐 03. Creating ELB (Elastic Load Balancer)

In this hands-on exercise, we will:

• Launch two EC2 instances.
• Deploy a simple web app using EC2 User Data.
• Create an Application Load Balancer (ALB) to distribute traffic between the two instances.
• Test load balancing and health checks.

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🧭 Architecture Diagram

[ Client Browser ]
        |
        ▼
[ 🌐 AWS Application Load Balancer ]
        |
 ┌──────────────┐
 ▼                 ▼
[ EC2 #1 ]    [ EC2 #2 ]
Hello World   Hello World

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⚙️ A. Launch EC2 Instances

🪜 Step 1: Go to the EC2 Console

• Navigate to EC2 → Instances → Launch Instances.

🪜 Step 2: Configure Instance Details

Setting	Value
Name	My First Instance
Amazon Machine Image (AMI)	Amazon Linux 2
Instance Type	t2.micro
Number of Instances	1
Key Pair	Proceed without a key pair

💡 Tip: Launch each EC2 instance separately, so you can choose a different Availability Zone for each (for example, ap-south-1a and ap-south-1b).

🪜 Step 3: Configure Network Settings

• Select existing security group → launch-wizard-1

• This group should already allow:

  • HTTP (port 80)
  • SSH (port 22)

🪜 Step 4: Add User Data (Web Server Script)

Scroll down to Advanced details → User Data and paste the following:

#!/bin/bash
yum update -y
yum install -y httpd
systemctl start httpd
systemctl enable httpd
echo "<h1>Hello World from $(hostname -f)</h1>" > /var/www/html/index.html

🪜 Step 5: Launch First Instance and Create AMI for Second

• Click Launch Instances to launch the first instance.

• Rename the launched instance to:

  • My First Instance

• After the first instance is running and configured, create an AMI from it:

  • Select the instance → Actions → Image and templates → Create image.
  • Give the image a name (for example, my-first-instance-ami) and create the image.

• Launch the second instance using the newly created AMI:

  • Navigate to Launch Instances → choose My AMIs → select my-first-instance-ami.

  • Configure Instance Type (t2.micro) and Network settings (choose the desired Availability Zone).

  • Proceed without a key pair if desired.

  • Launch and rename the second instance to:

    • My Second Instance

🪜 Step 6: Verify

• Wait for both instances to reach Running state.

• Copy each Public IPv4 address and open in a browser:

  • You should see:

    Hello World from ip-...

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⚖️ B. Create an Application Load Balancer (ALB)

🪜 Step 1: Navigate to Load Balancers

• Go to EC2 → Load Balancers → Create Load Balancer

🪜 Step 2: Select Type

Choose Application Load Balancer (ALB)

Type	Protocol	Use Case
Application Load Balancer	HTTP/HTTPS	Web traffic
Network Load Balancer	TCP/UDP	Ultra-low latency
Gateway Load Balancer	All	Firewalls, inspection tools

🪜 Step 3: Configure Basic Settings

Field	Value
Name	DemoALB
Scheme	Internet-facing
Address Type	IPv4

🪜 Step 4: Network Mapping

• Choose your VPC.
• Select All Availability Zones.

🪜 Step 5: Configure Security Group

• Create a new SG named demo-sg-load-balancer.
• Allow HTTP (port 80) from anywhere (0.0.0.0/0).
• Attach this SG to the ALB (remove the default one).

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🎯 Create Target Group

A Target Group is basically a collection of resources (targets) that your Load Balancer sends traffic to.

These “targets” are usually:

EC2 Instances ,Containers, IP Addresses, Lambda functions

Each target group tells AWS:

“Here’s where to send incoming requests that match certain rules.”

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🪜 Step 1: Create Target Group

• Type: Instances
• Name: demo-tg-alb
• Protocol: HTTP
• Port: 80
• Health Check Path: /

🪜 Step 2: Register Targets

• Select both EC2 instances.
• Click Include as pending below.
• Click Create Target Group.

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🚀 Attach Target Group to Load Balancer

• Go back to your ALB creation page.

• Under Listeners and Routing, choose:

  • Listener: HTTP on port 80
  • Target Group: demo-tg-alb

• Click Create Load Balancer.

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🔍 Test Load Balancing

🪜 Step 1: Wait for Provisioning

• Wait until ALB status = Active.
• Copy the DNS name (e.g., demoalb-123456.elb.amazonaws.com).

🪜 Step 2: Access the Load Balancer

• Open the DNS name in a browser.

• Refresh the page multiple times:

  • You’ll see the instance name changes.
  • ✅ Confirms load balancing is working.

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💚 Health Check and Fault Tolerance

🪜 Step 1: Check Target Health

• Go to Target Groups → demo-tg-alb → Targets.
• Both should show as Healthy.

🪜 Step 2: Simulate Failure

• Stop one instance.

• Refresh target group → it becomes Unhealthy/Unused.

• Refresh browser:

  • Traffic routes only to the healthy instance.

🪜 Step 3: Recovery

• Start the stopped instance.

• It will move from Initial → Healthy status.

• Refresh browser:

  • Requests will again alternate between both instances.

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✅ Summary

Component	Purpose
EC2 Instances	Host simple “Hello World” web app
Application Load Balancer	Distributes HTTP traffic
Target Group	Tracks instance health
Security Groups	Control inbound traffic
Health Checks	Detect unhealthy instances

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⚙️ Limitation

In this step, we are manually launching EC2 instances to understand how web servers are created and managed before automating the process later with Auto Scaling Groups (ASG).

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🧭 What We’re Doing

We’re:

• Manually launching two EC2 instances
• Installing Apache (httpd) using User Data
• Placing both behind a Load Balancer

This builds the base understanding of how individual servers are configured and connected.

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⚡ Why Manual Launch Isn’t Ideal

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Limitation	Explanation
❌ Manual scaling	You must add/remove instances by hand
❌ No fault recovery	If one instance fails, it won’t auto-restart
❌ Inefficient for traffic spikes	Load changes aren’t automatically handled

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🚀 Real-World Approach

In production, we use Auto Scaling Groups (ASG) with a Load Balancer to:

• Automatically launch instances across multiple AZs
• Replace unhealthy instances
• Scale up/down with traffic demand

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🧩 Big Picture

We’re doing it manually now to understand the building blocks.
Later, ASG + Load Balancer will automate everything we just did.