Terraform.tfvars file - Step-by-Step Execution

Process Flow - Terraform.tfvars file

Create variables.tf file

↓

Define variables with defaults or no defaults

↓

Create terraform.tfvars file

↓

Assign values to variables in terraform.tfvars

↓

Run terraform plan/apply

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Terraform reads terraform.tfvars and applies values

This flow shows how Terraform uses a terraform.tfvars file to assign values to variables defined in variables.tf during deployment.

Execution Sample

Terraform

variable "region" {
  description = "Cloud region"
  type        = string
}

# terraform.tfvars
region = "us-west-2"

Defines a variable 'region' and assigns it a value in terraform.tfvars for Terraform to use.

Process Table

Step	Action	File Read	Variable	Value Assigned	Effect
1	Terraform starts	variables.tf	region	no value yet	Variable declared, no value assigned
2	Terraform reads terraform.tfvars	terraform.tfvars	region	"us-west-2"	Value assigned to variable
3	Terraform plan/apply uses variable	N/A	region	"us-west-2"	Deployment uses assigned value
4	Execution ends	N/A	region	"us-west-2"	Process complete with variable set

💡 terraform.tfvars values loaded, variables assigned, deployment proceeds

Status Tracker

Variable	Start	After terraform.tfvars read	Final
region	undefined	"us-west-2"	"us-west-2"

Key Moments - 2 Insights

Why doesn't the variable have a value before terraform.tfvars is read?

Because variables are declared but not assigned until terraform.tfvars or other input sources provide values, as shown in step 1 and 2 of the execution_table.

What happens if terraform.tfvars does not include a variable value?

Terraform uses the default value if defined in variables.tf, or prompts the user if no default exists, since terraform.tfvars is just one way to assign values.

Visual Quiz - 3 Questions

Look at the execution_table, what value does 'region' have after reading terraform.tfvars?

A undefined

B "us-west-2"

C "us-east-1"

D null

💡 Hint

Check Step 2 in execution_table where terraform.tfvars is read and value assigned

At which step does Terraform use the variable value for deployment?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Effect' column in execution_table for when deployment uses the variable

If the terraform.tfvars file is missing, what will happen to the variable 'region'?

A It will remain undefined unless a default is set or user input is provided

B Terraform will assign a random value

C It will be assigned the value from terraform.tfvars anyway

D Terraform will fail immediately without any prompt

💡 Hint

Refer to key_moments about what happens if terraform.tfvars does not include a variable

Concept Snapshot

Terraform.tfvars file stores variable values separately from code.
Variables declared in variables.tf get values from terraform.tfvars.
Terraform reads terraform.tfvars automatically during plan/apply.
This separates config from code for easier management.
Missing values use defaults or prompt user.

Full Transcript

Terraform uses variables to customize deployments. Variables are declared in variables.tf files but start without values. The terraform.tfvars file assigns values to these variables. When Terraform runs, it reads variables.tf to know what variables exist, then reads terraform.tfvars to get their values. This process is shown step-by-step: first variables are declared, then terraform.tfvars is read to assign values, then Terraform uses these values to deploy resources. If terraform.tfvars is missing a variable, Terraform uses a default value if set or asks the user. This separation helps keep code clean and configuration flexible.

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