Understanding .tfvars in Terraform with Real EC2 Example

✅ What I Learned Today

Today, I focused on one of the most fundamental, yet often misunderstood features in Terraform: the use of .tfvars files. I explored it with hands-on EC2 deployment and captured the Terraform behavior clearly.

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🧠 Key Concepts Covered

• How .tfvars overrides variables.tf
• Real difference when changing EC2 instance_type
• When to use .tfvars and what to include in it
• Best practices to avoid pushing .tfvars to Git

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🔨 What I Did

1 Initial Setup

I created the following files inside a Terraform project:

```hcl

variables.tf

variable “instance_type” { default = “t2.micro” }

terraform.tfvars

instance_type = “t3.micro”

main.tf

resource “aws_instance” “web” { ami = var.ami_id instance_type = var.instance_type … }

2 Observing Terraform Behavior When I ran terraform plan, it showed: ~ instance_type = “t2.micro” -> “t3.micro” -/+ will be replaced Meaning: EC2 instance is immutable on instance_type change, so Terraform will destroy and recreate it.

3 Real-World Learning

• I noticed if I restart the EC2 manually from AWS Console, Terraform detects public IP changes even if infra wasn’t changed in code.
• If .tfvars has values, Terraform will always use them instead of variables.tf defaults.
• Variable Precedence Order (High → Low): CLI -var flag > CLI -var-file flag > terraform.tfvars file > *.auto.tfvars files > Environment variables > Default in variables.tf

📁 Folder Structure tf-infra-ec2/ ├── main.tf ├── variables.tf ├── terraform.tfvars ├── outputs.tf ├── terraform.tfstate

✅ Best Practices I Followed

- Keep .tfvars local and do not push to Git
- Use .tfvars.example in repo for team reference
- Override environment-specific values in .tfvars only
- Use terraform plan -var-file="dev.tfvars" in multi-env setups

🧪 Key Commands Used

- terraform init
- terraform plan -out=plan.out
- terraform apply "plan.out"
- terraform show

📚 My Takeaway Understanding .tfvars gives you confidence in clean separation of code vs config in Terraform. It’s a best practice that ensures clarity, reusability, and secure deployments in real teams and environments.

🚀 Next Step I’ll now create a new subproject using dev.tfvars and prod.tfvars to simulate multi-environment deployment.

Stay tuned & Happy reading...