Environment variables (TF_VAR_) in Terraform - Step-by-Step Execution

Process Flow - Environment variables (TF_VAR_)

Set environment variable TF_VAR_name=value

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Run terraform command

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Terraform reads environment variables

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Terraform maps TF_VAR_name to variable 'name'

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Variable 'name' gets value from environment

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Terraform applies configuration using variable value

Terraform reads environment variables starting with TF_VAR_ and uses their values to set input variables during execution.

Execution Sample

Terraform

export TF_VAR_region="us-west-2"
terraform apply

Sets the variable 'region' to 'us-west-2' via environment variable before running terraform apply.

Process Table

Step	Action	Environment Variable	Terraform Variable	Value Assigned
1	Set environment variable	TF_VAR_region=us-west-2	-	-
2	Run terraform apply	-	-	-
3	Terraform reads environment variables	TF_VAR_region=us-west-2	-	-
4	Map TF_VAR_region to variable 'region'	TF_VAR_region	region	us-west-2
5	Use variable 'region' in configuration	-	region	us-west-2

💡 Terraform completes apply using 'region' variable set from environment variable TF_VAR_region

Status Tracker

Variable	Start	After Step 4	Final
region	undefined	us-west-2	us-west-2

Key Moments - 3 Insights

Why does Terraform use the environment variable TF_VAR_region for the variable 'region'?

Terraform automatically maps environment variables starting with TF_VAR_ to input variables by removing the prefix. See execution_table row 4 where TF_VAR_region maps to 'region'.

What happens if the environment variable TF_VAR_region is not set?

The variable 'region' remains undefined unless set elsewhere (like in a tfvars file or default). Terraform will prompt or error if required. This is implied by the variable_tracker showing 'undefined' at start.

Can environment variables override variables set in files?

Yes, environment variables TF_VAR_ have higher precedence and override values from files. This is why Terraform reads environment variables first as shown in execution_table step 3.

Visual Quiz - 3 Questions

Look at the execution table, what value is assigned to the Terraform variable 'region' at step 4?

A us-west-2

B undefined

C TF_VAR_region

D null

💡 Hint

Check the 'Value Assigned' column at step 4 in the execution_table.

At which step does Terraform read the environment variables?

A Step 1

B Step 3

C Step 5

D Step 2

💡 Hint

Look at the 'Action' column in execution_table where Terraform reads environment variables.

If TF_VAR_region was not set, what would the variable_tracker show for 'region' after step 4?

A us-west-2

B null

C undefined

D empty string

💡 Hint

Refer to variable_tracker showing 'region' as 'undefined' before assignment.

Concept Snapshot

Terraform environment variables starting with TF_VAR_ set input variables.
Syntax: export TF_VAR_variableName=value
Terraform reads these before applying config.
They override variable defaults and tfvars files.
Use to pass sensitive or dynamic values easily.

Full Transcript

Terraform allows setting input variables using environment variables prefixed with TF_VAR_. For example, setting TF_VAR_region to 'us-west-2' assigns the variable 'region' this value during terraform apply. The flow starts by exporting the environment variable, then running terraform commands. Terraform reads these variables, maps them by removing the TF_VAR_ prefix, and uses the values in the configuration. If the environment variable is not set, the variable remains undefined unless set elsewhere. Environment variables override other variable sources, making them useful for dynamic or secret values.