Notes

Terraform Variables

3 min read

Interview Questions _ terraform

🧱 What are Terraform Variables? (Simple Meaning)

Terraform variables are inputs to your infrastructure code.

Instead of hard-coding values like region, VM size, or instance count, you parameterize them.

👉 Think of variables as function arguments for infrastructure.

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🔹 Why Variables Matter (Very Important)

Without variables ❌

instance_type = "t2.micro"

With variables ✅

instance_type = var.instance_type

Benefits

  • Reusable code
  • Easy environment switch (dev / prod)
  • Secure secrets handling
  • Industry best practice

1️⃣ Declaring a Variable (variables.tf)

Basic syntax:

variable "instance_type" {
  description = "EC2 instance type"
  type        = string
  default     = "t2.micro"
}

Key parts

FieldMeaning
variableVariable name
typeData type
defaultOptional fallback value
descriptionHuman-readable info

2️⃣ Using a Variable (main.tf)

resource "aws_instance" "demo" {
  ami           = "ami-0abcdef"
  instance_type = var.instance_type
}

👉 var. is mandatory to access variables.

3️⃣ Variable Types (VERY IMPORTANT)

🔸 String

variable "region" {
  type    = string
  default = "ap-south-1"
}

🔸 Number

variable "instance_count" {
  type    = number
  default = 2
}

Usage:

count = var.instance_count

🔸 Boolean

variable "enable_monitoring" {
  type    = bool
  default = true
}

🔸 List

variable "availability_zones" {
  type    = list(string)
  default = ["ap-south-1a", "ap-south-1b"]
}

Usage:

availability_zone = var.availability_zones[0]

🔸 Map (Very Common)

variable "instance_tags" {
  type = map(string)
  default = {
    Name = "DevServer"
    Env  = "Dev"
  }
}

Usage:

tags = var.instance_tags

4️⃣ Variable Without Default (Mandatory Input)

variable "db_password" {
  type      = string
  sensitive = true
}

Terraform will ask during apply:

terraform apply

5️⃣ Using terraform.tfvars (REAL WORLD)

Create file: terraform.tfvars

instance_type = "t3.medium"
instance_count = 3

Terraform auto-loads this file ✅

💡 Best practice:

  • variables.tf → definition
  • terraform.tfvars → values

6️⃣ Passing Variables via CLI

terraform apply -var="instance_type=t3.large"

Multiple:

terraform apply \
  -var="instance_type=t3.large" \
  -var="instance_count=2"

7️⃣ Environment-wise Variables (DevOps Style)

env/
 ├── dev.tfvars
 ├── prod.tfvars

terraform apply -var-file=env/dev.tfvars
terraform apply -var-file=env/prod.tfvars

🔥 This is how real companies manage infra.

8️⃣ Sensitive Variables (Security MUST)

variable "db_password" {
  type      = string
  sensitive = true
}

✔ Value hidden in logs
❌ Still stored in state file (use Vault later)

9️⃣ Output Variables (Bonus but Important)

output "public_ip" {
  value = aws_instance.demo.public_ip
}

After apply:

Outputs:
public_ip = 13.234.x.x

🔟 Common Beginner Mistakes ❌

MistakeFix
Hardcoding valuesUse variables
Forget var.Always prefix
Not typing variablesAlways define type
Secrets in codeUse sensitive vars
One tfvars for all envUse env-based files

🧠 Interview + Real Job Tip

If asked:

“How do you manage Terraform variables in production?”

Say:

“We define variables in variables.tf, store environment-specific values in separate .tfvars files, and pass secrets securely using CI/CD or secret managers.”

🔥 This answer sounds experienced.

📌 Your Practice Task (IMPORTANT)

Do this today:

  1. Create variables.tf
  2. Create main.tf
  3. Create terraform.tfvars
  4. Use string + number + map
  5. Run terraform plan

If you want, next I can teach:

  • Terraform locals
  • Variable validation
  • Modules with variables
  • Terraform variables for AKS / AWS
  • CKA + Terraform interview questions

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