Terraform Variables and Outputs: Making Your Infrastructure Configurable

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What Are Variables in Terraform?

Variables let you parameterize your configuration.

Instead of this:

region = "us-east-1"

You do this:

region = var.aws_region

And define the variable separately:

variable "aws_region" {
  type    = string
  default = "us-east-1"
}

Now you can override it in different ways — CLI, terraform.tfvars, or environment variables — making your config reusable, clean, and scalable.

Types of Variables

Terraform supports several types:

You can also use object, tuple, and any for advanced use cases.

🧪 Example: Defining a map

variable "ami_map" {
  type = map(string)
  default = {
    us-east-1 = "ami-123"
    us-west-2 = "ami-456"
  }
}

And using it:

ami = var.ami_map["us-east-1"]

How to Use .tfvars Files

Create a file called terraform.tfvars:

aws_region = "us-west-2"
instance_type = "t2.small"

Terraform will automatically load this file when you run terraform plan or apply.

You can also pass it explicitly:

terraform apply -var-file="dev.tfvars"

This is especially useful when working with multiple environments (dev, staging, prod).

What Are Outputs in Terraform?

Terraform outputs expose values from your configuration.

You can use them to:

• Display results (like IPs or IDs) after apply

• Pass values between modules

• Reference outputs in scripts or CI/CD tools

Here’s a basic example:

output "instance_ip" {
  value = aws_instance.web.public_ip
}

After terraform apply, Terraform will print the IP of the instance — very useful in pipelines or dashboards.

Hands-On Example: Dynamic Config with Variables and Outputs

Let’s put this all together.

Step 1: variables.tf

variable "aws_region" {
  type    = string
  default = "us-east-1"
}

variable "instance_type" {
  type    = string
  default = "t2.micro"
}

Step 2: main.tf

hcprovider "aws" {
  region = var.aws_region
}

resource "aws_instance" "web" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = var.instance_type
}l

Step 3: outputs.tf

output "instance_id" {
  value = aws_instance.web.id
}

Step 4: Run It

terraform init
terraform plan
terraform apply

You’ll see the instance_id printed on screen — dynamic, readable, and reusable infra code.

Common Pitfalls / Pro Tips

✅ Use terraform.tfvars for defaults, and override with env-specific files
 ✅ Validate variables using validation blocks (e.g., enforce naming rules)
 ✅ Use output values in scripts and CI/CD pipelines
 ❌ Don’t hardcode region, AMI, or environment-specific values

💡 Tip of the Day:

📚 Resources & References

1️⃣ Terraform Input Variables
🔗 Docs
Complete guide to declaring and using variables.

2️⃣ Terraform Output Values
🔗 Docs
How to expose and consume values from your infrastructure.

3️⃣ Validation Rules for Variables
🔗 Docs
Add logic to ensure variable input correctness.

4️⃣ Managing Multiple Environments with .tfvars
🔗 HashiCorp Learn
Practical examples for managing dev/staging/prod configs.

5️⃣ Working with Complex Variable Types
🔗 Advanced Guide
Explore maps, objects, and custom types in real use.

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