Variable validation rules in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of variable validation rules in Terraform?

Variable validation rules check if the input values meet certain conditions before applying changes. They help catch errors early and ensure correct configurations.

beginner

How do you define a validation rule for a variable in Terraform?

Inside the variable block, use the validation block with a condition expression and an error_message to explain the rule.

intermediate

Example: Write a validation rule that ensures a variable port is between 1024 and 65535.

validation { condition = var.port >= 1024 && var.port <= 65535 error_message = "Port must be between 1024 and 65535." }

beginner

What happens if a variable value does not meet the validation condition in Terraform?

Terraform stops the run and shows the error message defined in the validation block. This prevents applying invalid configurations.

intermediate

Can validation rules use complex expressions or functions in Terraform?

Yes, validation conditions can use any valid Terraform expressions and functions to create flexible and powerful checks.

Where do you place the validation rules for a variable in Terraform?

A Inside the variable block

B In the provider block

C In the output block

D In the terraform block

Validation rules are defined inside the variable block using the validation block.

What does Terraform do if a variable fails its validation rule?

A Automatically fixes the variable

B Ignores the error and continues

C Shows an error and stops the run

D Logs a warning but applies changes

Terraform stops execution and shows the error message to prevent invalid configurations.

Which of these is a valid validation condition for a string variable env to allow only 'dev', 'test', or 'prod'?

A contains(["dev", "test", "prod"], var.env)

B var.env == "dev" || var.env == "test" || var.env == "prod"

C var.env in ["dev", "test", "prod"]

D All of the above

All listed expressions correctly check if var.env is one of the allowed values.

What is the purpose of the error_message in a validation block?

A To describe the validation rule to users when it fails

B To fix the variable automatically

C To log the variable value

D To set a default value

The error_message explains why the validation failed to help users fix the input.

Can validation rules in Terraform use functions like length() or regex()?

A No, only simple comparisons are allowed

B Yes, any Terraform expression is allowed

C Only regex is allowed

D Only length() is allowed

Validation conditions can use any valid Terraform expressions and functions.

Explain how to add a validation rule to a Terraform variable and why it is useful.

Think about checking inputs before applying changes.

Describe what happens when a Terraform variable value does not meet its validation condition during a plan or apply.

Consider how Terraform protects your infrastructure.