Terraform.tfvars file - Commands & Configuration

Introduction

When you use Terraform to create cloud resources, you often need to provide values like names, sizes, or regions. The terraform.tfvars file helps you keep these values separate from your main setup so you can change them easily without touching the main code.

When you want to set specific values for your Terraform variables without changing the main configuration files.

When you have different environments like development and production and want to use different settings for each.

When you want to share your Terraform code but keep sensitive or environment-specific values separate.

When you want to quickly change resource names or sizes without editing multiple files.

When you want to keep your Terraform setup clean and organized by separating variable values.

Config File - terraform.tfvars

terraform.tfvars

region = "us-east-1"
instance_type = "t3.micro"
app_name = "my-app"
instance_count = 2

This file sets values for variables used in your Terraform configuration.

region: The cloud region where resources will be created.

instance_type: The size/type of the virtual machine.

app_name: A name to identify your application.

instance_count: How many instances to create.

Terraform automatically loads this file to apply these values during deployment.

Commands

This command prepares your Terraform working directory by downloading necessary plugins and setting up the environment.

Terminal

terraform init

Expected Output

Initializing the backend...



Initializing provider plugins...

- Finding latest version of hashicorp/aws...

- Installing hashicorp/aws v4.0.0...

- Installed hashicorp/aws v4.0.0 (signed by HashiCorp)



Terraform has been successfully initialized!

This command shows what Terraform will do based on your configuration and the values in terraform.tfvars, without making any changes yet.

Terminal

terraform plan

Expected Output

Refreshing Terraform state in-memory prior to plan...



An execution plan has been generated and is shown below.

Resource actions are indicated with the following symbols:

  + create



Terraform will perform the following actions:



  # aws_instance.my-app will be created

  + resource "aws_instance" "my-app" {

      + ami           = "ami-0c55b159cbfafe1f0"

      + instance_type = "t3.micro"

      + tags = {

          + "Name" = "my-app"

        }

    }



Plan: 1 to add, 0 to change, 0 to destroy.

This command applies the changes to create or update your cloud resources using the values from terraform.tfvars without asking for confirmation.

Terminal

terraform apply -auto-approve

Expected Output

aws_instance.my-app: Creating...

aws_instance.my-app: Still creating... [10s elapsed]

aws_instance.my-app: Creation complete after 20s [id=i-0abcd1234efgh5678]



Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

→

-auto-approve - Skips the confirmation prompt to apply changes immediately

This command shows the values of outputs defined in your Terraform configuration after deployment, confirming what was created.

Terminal

terraform output

Expected Output

instance_ip = "54.210.123.45"

Key Concept

If you remember nothing else from this pattern, remember: terraform.tfvars lets you set and change variable values separately from your main Terraform code for easy and safe configuration.

Common Mistakes

Not naming the file terraform.tfvars or using a different name without specifying it.

Terraform automatically loads terraform.tfvars but ignores other names unless explicitly told, so your values won't be applied.

Always name your variable values file terraform.tfvars or pass a different file with -var-file flag.

Putting syntax errors like missing quotes or wrong equals signs in terraform.tfvars.

Terraform will fail to read the file and stop with an error, blocking deployment.

Use correct syntax: key = "value" for strings, key = number for numbers, and check carefully.

Editing terraform.tfvars but forgetting to run terraform plan or apply again.

Changes won't take effect until you re-run Terraform commands to update your infrastructure.

After changing terraform.tfvars, always run terraform plan to see changes and terraform apply to apply them.

Summary

terraform.tfvars file holds variable values separately from main Terraform code.

terraform init sets up Terraform environment and plugins.

terraform plan shows what changes will happen using the variable values.

terraform apply creates or updates resources using those values.

terraform output displays information about created resources.

Practice

1. What is the main purpose of the terraform.tfvars file in a Terraform project?

easy

A. To store Terraform state files

B. To define the Terraform provider configuration

C. To write the main infrastructure resources

D. To store values for variables separately from the main Terraform code

Solution

1. Step 1: Understand the role of terraform.tfvars

   This file is used to provide values for variables declared in Terraform configuration files, keeping values separate from code.

2. Step 2: Differentiate from other files

   Provider configuration and resource definitions are in .tf files, and state files are managed separately, not in terraform.tfvars.

3. Final Answer:

   To store values for variables separately from the main Terraform code -> Option D

4. Quick Check:

   Variable values stored separately = D [OK]

Hint: Remember: tfvars holds variable values, not code or state [OK]

Common Mistakes:

• Confusing tfvars with provider or resource files
• Thinking tfvars stores state files
• Assuming tfvars contains resource definitions

2. Which of the following is the correct syntax to assign a list of strings in a terraform.tfvars file?

easy

A. my_list = {"apple", "banana", "cherry"}

B. my_list = ("apple", "banana", "cherry")

C. my_list = ["apple", "banana", "cherry"]

D. my_list = "apple", "banana", "cherry"

Solution

1. Step 1: Identify list syntax in tfvars

   Terraform uses square brackets [] to define lists in tfvars files.

2. Step 2: Check each option

   my_list = ["apple", "banana", "cherry"] uses square brackets with quoted strings, which is correct. Options B and C use parentheses or curly braces, which are invalid for lists. my_list = "apple", "banana", "cherry" is missing brackets.

3. Final Answer:

   my_list = ["apple", "banana", "cherry"] -> Option C

4. Quick Check:

   Lists use square brackets [] = A [OK]

Hint: Lists always use square brackets [] in tfvars [OK]

Common Mistakes:

• Using parentheses or curly braces instead of square brackets
• Forgetting quotes around string items
• Omitting brackets entirely

3. Given the following terraform.tfvars content:

region = "us-west-2"
instance_count = 3
enable_backup = true
allowed_ips = ["10.0.0.1", "10.0.0.2"]

What is the value and type of enable_backup when accessed in Terraform?

medium

A. String "true"

B. Boolean true

C. Number 1

D. List with one element "true"

Solution

1. Step 1: Identify the value type in tfvars

   The value enable_backup = true is a boolean literal, not a string or number.

2. Step 2: Understand Terraform variable typing

   Terraform reads true as a boolean true, not as a string or number.

3. Final Answer:

   Boolean true -> Option B

4. Quick Check:

   Boolean literals stay boolean = B [OK]

Hint: True/false without quotes are booleans in tfvars [OK]

Common Mistakes:

• Treating true as a string by adding quotes
• Assuming true converts to number 1
• Confusing boolean with list type

4. You wrote this in your terraform.tfvars file:

max_instances = 5
allowed_ports = [80, 443, 22

When running Terraform, you get a syntax error. What is the most likely cause?

medium

A. Missing closing bracket for the list

B. Using numbers instead of strings in the list

C. Variable names cannot have underscores

D. The equals sign should be a colon

Solution

1. Step 1: Check list syntax carefully

   The list allowed_ports is opened with [ but the snippet ends after 22 with no closing ].

2. Step 2: Identify syntax error

   The list lacks a closing bracket, causing the syntax error. Other options are invalid: underscores are allowed, numbers are fine in lists, and = is correct syntax.

3. Final Answer:

   Missing closing bracket for the list -> Option A

4. Quick Check:

   Lists must have matching brackets = C [OK]

Hint: Always count opening and closing brackets in lists [OK]

Common Mistakes:

• Forgetting to close lists with a bracket
• Thinking numbers must be strings
• Using colons instead of equals

5. You want to use a map variable in your Terraform configuration to assign different instance types per environment. Which terraform.tfvars content correctly assigns instance types for "dev" and "prod" environments?

hard

A. instance_types = { dev = "t2.micro", prod = "t2.large" }

B. instance_types = ["dev" = "t2.micro", "prod" = "t2.large"]

C. instance_types = (dev: "t2.micro", prod: "t2.large")

D. instance_types = { "dev", "t2.micro", "prod", "t2.large" }

Solution

1. Step 1: Understand map syntax in tfvars

   Maps use curly braces {} with key = value pairs, keys and values can be strings.

2. Step 2: Evaluate each option

   instance_types = { dev = "t2.micro", prod = "t2.large" } correctly uses curly braces with keys and values separated by =. instance_types = ["dev" = "t2.micro", "prod" = "t2.large"] uses square brackets and equals inside, which is invalid. instance_types = (dev: "t2.micro", prod: "t2.large") uses parentheses and colons, invalid syntax. instance_types = { "dev", "t2.micro", "prod", "t2.large" } uses curly braces but with commas separating keys and values without equals, invalid.

3. Final Answer:

   instance_types = { dev = "t2.micro", prod = "t2.large" } -> Option A

4. Quick Check:

   Maps use curly braces with key = value pairs = A [OK]

Hint: Maps use curly braces with key = value pairs in tfvars [OK]

Common Mistakes:

• Using square brackets for maps
• Using colons instead of equals
• Separating keys and values with commas only