Modules for reusability in GCP - Step-by-Step Execution

Process Flow - Modules for reusability

Create Module Files

↓

Define Resources & Variables

↓

Use Module in Main Config

↓

Pass Inputs to Module

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Terraform Init & Apply

↓

Module Creates Resources

↓

Reuse Module Anywhere

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END

This flow shows how you create a module, define its resources, use it in your main config, pass inputs, and deploy reusable infrastructure.

Execution Sample

GCP

module "vm_instance" {
  source = "./modules/vm"
  name   = "my-vm"
  zone   = "us-central1-a"
}

This code uses a module to create a VM instance with reusable parameters for name and zone.

Process Table

Step	Action	Input/Variable	Result/State Change
1	Create module directory and files	modules/vm/main.tf, variables.tf	Module files ready with resource and variables defined
2	Define variables in module	var.name, var.zone	Variables declared for module inputs
3	Write resource using variables	google_compute_instance with var.name and var.zone	Resource template ready for reuse
4	In main config, call module with source and inputs	source=./modules/vm, name=my-vm, zone=us-central1-a	Module block added to main config
5	Run terraform init	Initialize modules	Modules downloaded and initialized
6	Run terraform apply	Apply config	VM instance created with name=my-vm in zone=us-central1-a
7	Reuse module with different inputs	name=your-vm, zone=us-east1-b	Another VM created with new inputs
8	Exit	No more modules to apply	Infrastructure deployed with reusable modules

💡 All modules applied and resources created; no more modules to process.

Status Tracker

Variable	Start	After Step 4	After Step 6	After Step 7	Final
var.name	undefined	my-vm	my-vm	your-vm	your-vm
var.zone	undefined	us-central1-a	us-central1-a	us-east1-b	us-east1-b

Key Moments - 3 Insights

Why do we define variables inside the module instead of hardcoding values?

Variables allow the module to accept different inputs each time it is used, making it reusable with different configurations as shown in steps 2 and 7.

What happens if we forget to run 'terraform init' after adding a module?

'terraform init' downloads and initializes modules. Without it, Terraform cannot use the module source, so apply will fail (see step 5).

Can we use the same module multiple times with different inputs?

Yes, as shown in step 7, reusing the module with different inputs creates separate resources without rewriting code.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of var.name after step 6?

A my-vm

B your-vm

C undefined

D us-central1-a

💡 Hint

Check variable_tracker row for var.name at After Step 6 column.

At which step does Terraform initialize the modules?

A Step 4

B Step 6

C Step 5

D Step 7

💡 Hint

Look at the Action column in execution_table for 'terraform init'.

If you want to create a VM in a new zone, which step shows how to do it?

A Step 4

B Step 7

C Step 2

D Step 6

💡 Hint

Step 7 shows reusing the module with different inputs.

Concept Snapshot

Modules let you package infrastructure code for reuse.
Define variables inside modules for flexibility.
Call modules in main config with inputs.
Run 'terraform init' to prepare modules.
Apply creates resources from module code.
Reuse modules by changing inputs only.

Full Transcript

Modules for reusability in GCP Terraform let you write infrastructure code once and use it many times with different inputs. First, you create module files defining resources and variables. Then, in your main configuration, you call the module and pass values for those variables. Running 'terraform init' downloads and prepares the module. Applying the configuration creates the resources. You can reuse the same module multiple times by passing different inputs, saving time and avoiding repeated code.