Why load balancing matters in AWS - See It in Action

Why Load Balancing Matters

📖 Scenario: You are setting up a simple web service on AWS. You want to make sure your website stays online and fast even if many people visit at the same time. To do this, you will create a load balancer that shares the visitors' requests across multiple servers.

🎯 Goal: Build an AWS Elastic Load Balancer configuration that distributes traffic evenly to two web servers, ensuring better availability and performance.

📋 What You'll Learn

Create two EC2 instances with a simple web server

Create an Elastic Load Balancer (ELB) that listens on port 80

Register the two EC2 instances with the ELB

Configure health checks for the ELB to monitor instance health

💡 Why This Matters

🌍 Real World

Load balancing helps websites and apps stay fast and available when many users visit at once by sharing the work across multiple servers.

💼 Career

Understanding load balancing is essential for cloud engineers and architects to design scalable and reliable cloud applications.

1

Create two EC2 instances

Create two EC2 instances named web-server-1 and web-server-2 using the Amazon Linux 2 AMI. Both instances should be in the us-east-1a availability zone.

AWS

# Your code here to create two EC2 instances named web-server-1 and web-server-2

Hint

Use resource "aws_instance" to create EC2 instances and set the tags block with the Name key.

2

Create an Elastic Load Balancer

Create an AWS Elastic Load Balancer named web-elb that listens on port 80 for HTTP traffic.

AWS

resource "aws_instance" "web_server_1" {
  ami           = "ami-0c02fb55956c7d316"
  instance_type = "t2.micro"
  availability_zone = "us-east-1a"
  tags = {
    Name = "web-server-1"
  }
}

resource "aws_instance" "web_server_2" {
  ami           = "ami-0c02fb55956c7d316"
  instance_type = "t2.micro"
  availability_zone = "us-east-1a"
  tags = {
    Name = "web-server-2"
  }
}

# Your code here to create an Elastic Load Balancer named web-elb listening on port 80

Hint

Use resource "aws_elb" and define a listener block with ports set to 80.

3

Register EC2 instances with the Load Balancer

Register the two EC2 instances web-server-1 and web-server-2 with the Elastic Load Balancer web-elb using the instances attribute.

AWS

resource "aws_instance" "web_server_1" {
  ami           = "ami-0c02fb55956c7d316"
  instance_type = "t2.micro"
  availability_zone = "us-east-1a"
  tags = {
    Name = "web-server-1"
  }
}

resource "aws_instance" "web_server_2" {
  ami           = "ami-0c02fb55956c7d316"
  instance_type = "t2.micro"
  availability_zone = "us-east-1a"
  tags = {
    Name = "web-server-2"
  }
}

resource "aws_elb" "web_elb" {
  name               = "web-elb"
  listener {
    instance_port     = 80
    instance_protocol = "http"
    lb_port           = 80
    lb_protocol       = "http"
  }
  availability_zones = ["us-east-1a"]

  # Your code here to register instances
}

Hint

Add the instances attribute inside the ELB resource and list the instance IDs.

4

Configure health checks for the Load Balancer

Add a health_check block to the Elastic Load Balancer web-elb that checks the path / on port 80 every 30 seconds with a timeout of 5 seconds and considers an instance healthy after 2 successful checks.

AWS

resource "aws_instance" "web_server_1" {
  ami           = "ami-0c02fb55956c7d316"
  instance_type = "t2.micro"
  availability_zone = "us-east-1a"
  tags = {
    Name = "web-server-1"
  }
}

resource "aws_instance" "web_server_2" {
  ami           = "ami-0c02fb55956c7d316"
  instance_type = "t2.micro"
  availability_zone = "us-east-1a"
  tags = {
    Name = "web-server-2"
  }
}

resource "aws_elb" "web_elb" {
  name               = "web-elb"
  listener {
    instance_port     = 80
    instance_protocol = "http"
    lb_port           = 80
    lb_protocol       = "http"
  }
  availability_zones = ["us-east-1a"]
  instances          = [aws_instance.web_server_1.id, aws_instance.web_server_2.id]

  # Your code here to add health_check block
}

Hint

Add a health_check block inside the ELB resource with the specified settings.

Practice

1. What is the main purpose of a load balancer in AWS?

easy

A. To create backups of servers automatically

B. To store user data securely

C. To distribute incoming traffic evenly across multiple servers

D. To monitor server CPU usage only

Solution

1. Step 1: Understand load balancer role

   A load balancer shares user traffic across servers to keep apps fast and reliable.

2. Step 2: Identify main function

   Its main job is to distribute incoming traffic evenly to avoid overloading one server.

3. Final Answer:

   To distribute incoming traffic evenly across multiple servers -> Option C

4. Quick Check:

   Load balancer = distribute traffic [OK]

Hint: Load balancer spreads traffic to avoid overload [OK]

Common Mistakes:

• Confusing load balancer with data storage
• Thinking it only monitors CPU
• Assuming it creates backups

2. Which AWS service is used to create a load balancer?

easy

A. Amazon S3

B. Elastic Load Balancing (ELB)

C. Amazon RDS

D. AWS Lambda

Solution

1. Step 1: Identify AWS services

   Amazon S3 stores files, RDS manages databases, Lambda runs code, ELB manages load balancing.

2. Step 2: Match service to load balancing

   Elastic Load Balancing (ELB) is the AWS service designed to create load balancers.

3. Final Answer:

   Elastic Load Balancing (ELB) -> Option B

4. Quick Check:

   Load balancer service = ELB [OK]

Hint: ELB is the AWS load balancer service name [OK]

Common Mistakes:

• Choosing storage or compute services instead of ELB
• Confusing Lambda with load balancing
• Selecting database services

3. Given this AWS setup code snippet, what does the load balancer do?

LoadBalancer -> TargetGroup -> EC2 Instances
Listener listens on port 80 and forwards to TargetGroup

medium

A. It forwards traffic on port 80 to all EC2 instances evenly

B. It blocks traffic on port 80

C. It stores data from EC2 instances

D. It only forwards traffic to one EC2 instance

Solution

1. Step 1: Understand listener role

   The listener listens on port 80 and forwards requests to the target group.

2. Step 2: Understand target group role

   The target group contains multiple EC2 instances and the load balancer distributes traffic evenly among them.

3. Final Answer:

   It forwards traffic on port 80 to all EC2 instances evenly -> Option A

4. Quick Check:

   Listener + TargetGroup = distribute traffic [OK]

Hint: Listener forwards traffic evenly to all targets [OK]

Common Mistakes:

• Thinking it blocks traffic
• Assuming it stores data
• Believing it sends traffic to only one instance

4. You set up a load balancer but all traffic goes to a single server. What is the likely mistake?

medium

A. Security group blocks all traffic

B. Listener is set to forward on wrong port

C. Load balancer is not created

D. Target group has only one instance registered

Solution

1. Step 1: Check target group configuration

   If only one instance is registered in the target group, all traffic goes to that instance.

2. Step 2: Verify listener and load balancer existence

   Listener forwarding on wrong port or missing load balancer would cause no traffic or errors, not single server traffic.

3. Final Answer:

   Target group has only one instance registered -> Option D

4. Quick Check:

   Single server traffic = one target instance [OK]

Hint: Check target group instance count first [OK]

Common Mistakes:

• Assuming listener port causes single server traffic
• Thinking load balancer absence sends traffic
• Blaming security group for traffic routing

5. You want to handle sudden traffic spikes without slowing your app. Which load balancing setup helps best?

hard

A. Use a load balancer with multiple target groups and auto-scaling EC2 instances

B. Use a single EC2 instance behind a load balancer

C. Use only one target group with fixed number of instances

D. Disable load balancer and rely on DNS round robin

Solution

1. Step 1: Understand traffic spike handling

   Handling spikes requires scaling resources automatically to meet demand.

2. Step 2: Match setup to scaling needs

   Using a load balancer with multiple target groups and auto-scaling EC2 instances allows dynamic resource adjustment and balanced traffic.

3. Final Answer:

   Use a load balancer with multiple target groups and auto-scaling EC2 instances -> Option A

4. Quick Check:

   Auto-scaling + load balancer = handle spikes [OK]

Hint: Combine load balancer with auto-scaling for spikes [OK]

Common Mistakes:

• Relying on single instance for heavy traffic
• Using fixed instances without scaling
• Disabling load balancer reduces reliability