Default values in Terraform - Step-by-Step Execution

Process Flow - Default values

Start variable declaration

↓

Check if input value provided?

No→Use default value

Yes↓

Use provided input value

↓

Variable value set

↓

End

Terraform variables check if a user input is given; if not, they use the default value specified.

Execution Sample

Terraform

variable "region" {
  type    = string
  default = "us-west-1"
}

output "selected_region" {
  value = var.region
}

Defines a variable with a default region; outputs the selected region value.

Process Table

Step	Input Provided?	Variable Value Set	Output Value
1	No	"us-west-1" (default)	"us-west-1"
2	Yes (e.g., "eu-central-1")	"eu-central-1"	"eu-central-1"

💡 Execution ends after variable value is set and output is produced.

Status Tracker

Variable	Start	After No Input	After Input Provided
var.region	undefined	"us-west-1"	"eu-central-1"
output.selected_region	undefined	"us-west-1"	"eu-central-1"

Key Moments - 2 Insights

What happens if no value is provided for the variable?

Terraform uses the default value specified in the variable block, as shown in execution_table row 1.

Can the default value be overridden?

Yes, if a value is provided during terraform apply or in a tfvars file, it overrides the default, as shown in execution_table row 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the variable value when no input is provided?

A undefined

B "eu-central-1"

C "us-west-1"

D null

💡 Hint

Check execution_table row 1 under 'Variable Value Set'

At which step does the variable value get overridden by user input?

A Step 2

B Step 1

C Never

D Before Step 1

💡 Hint

See execution_table row 2 where input is provided

If the default value is removed, what happens when no input is provided?

A Terraform uses null as value

B Terraform throws an error

C Terraform uses an empty string

D Terraform uses a random value

💡 Hint

Default values prevent errors when no input is given; removing default causes error if no input

Concept Snapshot

Terraform variables can have default values.
If no input is given, Terraform uses the default.
User input overrides the default value.
Defaults prevent errors from missing inputs.
Use 'default = value' inside variable blocks.

Full Transcript

In Terraform, variables can have default values. When Terraform runs, it checks if the user provided a value for the variable. If not, it uses the default value specified. If the user provides a value, that value overrides the default. This behavior ensures Terraform has a value to use and avoids errors from missing inputs. The example shows a variable 'region' with a default of 'us-west-1'. If no input is given, Terraform uses 'us-west-1'. If the user provides 'eu-central-1', Terraform uses that instead. Removing the default without providing input causes an error.