Understanding Interpolation in Terraform with EC2 Example

 By Raees Qazi | DevOps Engineer | Learner | Mentor | Creator

Today, let’s understand what interpolation is and how we can create an EC2 instance using Terraform while extracting values using interpolation.

This guide is going to be simple and practical — no jargon, just real working code.

💡 Prerequisites

Before we begin, I’m assuming:

• You have already created the provider.tf file.
• Terraform is initialized (terraform init already run).
• AWS CLI is configured with an IAM user.

If all of the above is done, let’s move to the next step.

🛠 Create EC2 Instance with Terraform

Now, we’ll create a file named ec2.tf and write our resource configuration.

# ec2.tf
resource "aws_instance" "my_instance" {
  count         = 2                         # How many machines you want to create
  ami           = "ami-xxxxxxxxxxxxxxxxx"   # Replace with a valid AMI ID for your region
  instance_type = "t2.micro"                # Type of instance
  key_name      = "private-key"             # Use an existing key pair name
  tags = {
    Name = "My-Auto-server"                 # Name tag for the instance
  }
}
output "my_ec2_ip" {
  value = aws_instance.my_instance[0].public_ip
}

🧠 Explanation

• Resource Block:
   We define a resource of type aws_instance with the name my_instance.
   The count = 2 means Terraform will create two EC2 machines.
• Tags:
   We’re giving the instance a tag "Name" = "My-Auto-server" so it’s easy to identify in the AWS console.
• AMI:
   Every EC2 machine is created from an Amazon Machine Image (AMI). You must provide a valid AMI ID according to your region.
• Instance Type:
   t2.micro is a free-tier eligible instance type, perfect for testing and learning.
• Key Name:
   Here you define the name of your existing EC2 key pair to enable SSH access.

🔁 Interpolation in Action

Look at this block:

output "my_ec2_ip" {
  value = aws_instance.my_instance[0].public_ip
}

Here we are using interpolation to access a value from the Terraform object.

• aws_instance.my_instance → refers to our EC2 resource.
• [0] → since we created 2 instances, we’re getting the first one (index starts from 0).
• .public_ip → this fetches the public IP of that instance.

This is called interpolation — it allows you to reference values dynamically from other resources in Terraform.

🚀 Deploy the Infrastructure

Once your ec2.tf is ready, simply run:

terraform plan
terraform apply

Wait a few moments…

✨ Jaddo is in front of you! ✨
 Your EC2 machines are created and the public IP of the first instance is displayed on your screen — thanks to the output block.

📣 Final Words

That’s it — simple and clear!

We understood:

• What interpolation is in Terraform.
• How to create multiple EC2 instances.
• How to extract values like public IP using interpolation.

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By Raees Qazi
 DevOps Engineer | Learner | Mentor | Creator