Module outputs in Terraform - Step-by-Step Execution

Process Flow - Module outputs

Define output in module

↓

Run terraform apply

↓

Terraform processes module

↓

Module generates output value

↓

Output value available to root module

↓

Use output in root module or display

This flow shows how a Terraform module defines outputs, which are then produced during apply and made available to the root module or user.

Execution Sample

Terraform

module "example" {
  source = "./example_module"
}

output "instance_ip" {
  value = module.example.instance_ip
}

This code calls a module and outputs the instance IP address that the module provides.

Process Table

Step	Action	Evaluation	Result
1	Terraform reads root module	Finds module block	Prepares to call example_module
2	Terraform enters example_module	Processes resources	Creates instance with IP 10.0.0.5
3	Module output 'instance_ip' evaluated	Reads instance IP	Value is 10.0.0.5
4	Terraform returns output to root	Assigns module.example.instance_ip	Value 10.0.0.5 available
5	Root module output 'instance_ip' evaluated	Reads module output	Outputs 10.0.0.5 to user
6	Terraform apply completes	Outputs displayed	instance_ip = 10.0.0.5

💡 Terraform apply finishes after outputs are displayed to the user.

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
module.example.instance_ip	undefined	undefined	10.0.0.5	10.0.0.5	10.0.0.5
output.instance_ip	undefined	undefined	undefined	undefined	10.0.0.5

Key Moments - 2 Insights

Why does the output value only appear after terraform apply?

Because the module resources must be created first to have real values; see execution_table step 2 and 3 where the instance IP is assigned during apply.

Can outputs from a module be used inside the same module?

No, outputs are only available to the root or calling module after apply, not inside the module itself; outputs are for passing data out.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of module.example.instance_ip after step 3?

A 10.0.0.5

B null

C undefined

D module output not yet evaluated

💡 Hint

Check the 'Result' column at step 3 in the execution_table.

At which step does the root module output 'instance_ip' become available to the user?

A Step 4

B Step 5

C Step 2

D Step 6

💡 Hint

Look for when the root module output is evaluated in the execution_table.

If the module did not define an output, what would happen to the root module output referencing it?

A It would show null

B It would show an empty string

C Terraform would error during apply

D It would show the resource ID

💡 Hint

Outputs must be defined in the module to be accessible; see key_moments about output availability.

Concept Snapshot

Terraform module outputs:
- Defined inside modules with 'output' blocks
- Provide values from module to root module
- Available only after 'terraform apply'
- Used to share info like IPs, IDs
- Cannot be used inside the same module
- Accessed as module.<name>.<output>

Full Transcript

This visual execution shows how Terraform module outputs work. First, Terraform reads the root module and finds a module block. It then processes the module's resources, creating infrastructure like an instance with an IP address. The module defines an output that reads this IP. After creation, Terraform assigns this output value to the root module's reference. Finally, the root module outputs the value to the user after apply completes. Outputs are only available after resources exist and cannot be used inside the module itself. This flow helps pass information from modules back to the root or other modules.