Input variable precedence order in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Variable Precedence in Terraform

In Terraform, multiple sources can provide values for input variables. Which source has the highest precedence when determining the final value of a variable?

A A value passed directly via the command line using -var

B A default value defined in the variable block

C A value set in environment variables with the TF_VAR_ prefix

D A value set in a terraform.tfvars file

💡 Hint

Think about which method directly overrides others when running Terraform commands.

Values passed directly via the command line using -var have the highest precedence and override values from tfvars files, environment variables, and defaults.

🧠 Conceptual

intermediate

Order of Variable Sources in Terraform

Arrange the following Terraform variable sources from highest to lowest precedence:

• Default value in variable block
• Environment variable with TF_VAR_ prefix
• Command line -var option
• terraform.tfvars file

A 3,4,2,1

B 3,2,4,1

C 4,3,2,1

D 2,3,4,1

💡 Hint

Remember that command line options override environment variables, which override tfvars files, which override defaults.

The correct order from highest to lowest precedence is: command line -var option, environment variables with TF_VAR_ prefix, terraform.tfvars file, then default values.

❓ service_behavior

advanced

Effect of Multiple Variable Sources on Terraform Plan

You have a variable region with a default value of us-east-1. You set an environment variable TF_VAR_region=us-west-2 and also pass -var='region=eu-central-1' on the command line. What region will Terraform use during the plan?

A us-east-1

B us-west-2

C Terraform will throw an error due to conflicting values

D eu-central-1

💡 Hint

Which input source has the highest priority?

The command line -var option overrides environment variables and default values, so Terraform uses eu-central-1.

❓ security

advanced

Security Implications of Variable Precedence

Which Terraform variable input method is the safest to store sensitive data like passwords, considering variable precedence and exposure risk?

A Using environment variables with TF_VAR_ prefix

B Storing sensitive data in terraform.tfvars file checked into version control

C Passing sensitive data via command line -var option

D Defining sensitive data as default values in variable blocks

💡 Hint

Consider which method avoids exposing secrets in command history or version control.

Using environment variables with TF_VAR_ prefix is safer because it avoids storing secrets in files or command history, reducing exposure risk.

❓ Architecture

expert

Resolving Variable Conflicts in Terraform Modules

You have a root module and a child module. The root module passes a variable instance_type with value t3.micro via -var. The child module has a variable instance_type with a default t2.small. The root module also sets instance_type in a terraform.tfvars file as t3a.small. Which instance_type value will the child module receive during apply?

A t3a.small

B Terraform will fail due to conflicting variable values

C t3.micro

D t2.small

💡 Hint

Remember how variable values are passed from root to child modules and the precedence of input sources.

The root module's command line -var option overrides the terraform.tfvars file and default values. The child module receives the value passed from the root module, which is t3.micro.