Module inputs (variables) in Terraform - Step-by-Step Execution

Process Flow - Module inputs (variables)

Define variable in module

↓

Call module with input values

↓

Terraform reads input values

↓

Module uses inputs to create resources

↓

Outputs reflect resource state based on inputs

Terraform modules receive input values through variables defined inside the module and passed when calling the module. These inputs control resource creation.

Execution Sample

Terraform

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

module "example" {
  source = "./modules/example"
  region = "us-west-2"
}

Defines a variable 'region' with default, then calls a module passing a different region value.

Process Table

Step	Action	Variable	Value	Effect
1	Define variable 'region' with default	region	us-east-1	Variable ready with default
2	Call module 'example' passing region	region	us-west-2	Input overrides default
3	Terraform reads module input	region	us-west-2	Module uses passed value
4	Module creates resources using region	region	us-west-2	Resources created in us-west-2
5	Module outputs reflect resource state	region	us-west-2	Outputs show resources in us-west-2
6	Execution ends	-	-	All inputs processed, resources created

💡 Module inputs processed; resources created using passed variable values

Status Tracker

Variable	Defined	Passed to Module	Used in Module	Final
region	us-east-1 (default)	us-west-2	us-west-2	us-west-2

Key Moments - 2 Insights

Why does the module use 'us-west-2' instead of the default 'us-east-1'?

Because the module call passes 'region = "us-west-2"', which overrides the variable's default value as shown in execution_table step 2 and 3.

What happens if no value is passed to the module for 'region'?

Terraform uses the variable's default value 'us-east-1' inside the module, as defined in step 1.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what value does the module variable 'region' have?

A us-east-1

B undefined

C us-west-2

D null

💡 Hint

Check the 'Value' column at step 3 in the execution_table

At which step does Terraform read the input value passed to the module?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look for the step where Terraform reads module input in the execution_table

If the module call did not pass any value for 'region', what would be the final value used inside the module?

A null

B us-east-1

C us-west-2

D empty string

💡 Hint

Refer to variable_tracker and key_moments about default values

Concept Snapshot

Terraform modules use variables to accept inputs.
Variables have defaults but can be overridden when calling the module.
Passed values replace defaults inside the module.
Modules use these inputs to create resources.
Outputs reflect the resource state based on inputs.

Full Transcript

In Terraform, modules can accept inputs through variables defined inside them. These variables can have default values. When you call a module, you can pass values to these variables, which override the defaults. Terraform reads these input values during execution and uses them to create resources inside the module. The outputs from the module then reflect the state of these resources based on the inputs provided. This process allows modules to be reusable and configurable by changing input values without modifying the module code.