GCP Google Cloud Platform - Terraform Input Variables and Output Values

Step-01: Introduction

Terraform Concepts

• Terraform Input Variables
• Terraform Output Values

What are we going to learn ?

1. Learn about Terraform Input Variable basics
2. gcp_project
3. gcp_region
4. machine_type
5. Learn about Terraform Output Values
6. vm_instanceid
7. vm_selflink
8. vm_id
9. vm_name
10. vm_machine_type

Step-02: c2-variables.tf - Define Input Variables in Terraform

• Terraform Input Variables

  # GCP Project
  variable "gcp_project" {
    description = "Project in which GCP Resources to be created"
    type = string
    default = "gcplearn9"
  }
  
  # GCP Region
  variable "gcp_region" {
    description = "Region in which GCP Resources to be created"
    type = string
    default = "us-central1"
  }
  
  # GCP Compute Engine Machine Type
  variable "machine_type" {
    description = "Compute Engine Machine Type"
    type = string
    default = "e2-micro"
  }
  

Step-03: Reference the variables in respective .tffies

# c1-versions.tf
provider "google" {
  project = var.gcp_project
  region = var.gcp_region
}

# c3-vpc.tf
resource "google_compute_subnetwork" "mysubnet" {
  name = "${var.gcp_region1}-subnet"
  region = var.gcp_region1
  ip_cidr_range = "10.128.0.0/20"
  network = google_compute_network.myvpc.id 
}

# c5-vminstance.tf
resource "google_compute_instance" "myvm" {
  name         = "myvm1"
  machine_type = var.machine_type
  zone         = var.gcp_region1

Step-04: Variable Definition Option: terraform.tfvars

• We can define the variables

  # terraform.tfvars
  gcp_project   = "gcplearn9"
  gcp_region1   = "us-central1"
  machine_type  = "e2-micro"
  
  # Execute Terraform Commands
  # Terraform Init
  terraform init
  
  # Terraform Validate
  terraform validate
  
  # Terraform Plan
  terraform plan
  Observation:
  1. Review VM Instance machine_type
  2. It should be loaded from terraform.tfvars
  

Step-06: Variable Definition Option: vm.auto.tfvars

# vm.auto.tfvars
machine_type  = "e2-medium"

# Terraform Plan
terraform plan
Observation:
1. Review VM Instance machine_type
2. It should be loaded from vm.auto.tfvars
3. So, so far we have seen three ways
3.1 vm.auto.tfvars - First Priority
3.2 terraform.tfvars - Second Priority
3.3 variables.tf - default value defined in variables.tf

Step-07: Variable Definition Option: vm.tfvars

# vm.tfvars
machine_type  = "e2-standard-8"

# Terraform Plan
terraform plan
Observation:
1. Review VM Instance machine_type
2. It should be loaded from vm.auto.tfvars
3. We need to explicity pass the vm.tfvars to terraform commands

# Terraform plan
terraform plan --var-file=vm.tfvars
Observation:
1. Review VM Instance machine_type
2. It should be loaded from vm.tfvars whose value is e2-standard-8
3. In short, what-ever we pass via --var-file or --var flags will be having higher priority than anyother options

Step-07: Variable Definition Option: Directly pass it in command

# Terraform plan
terraform plan --var=machine_type=e2-standard-4
Observation:
1. Review VM Instance machine_type
2. It should be loaded from the command whose value is e2-standard-4

Step-08: Comment values in vm.auto.tfvars and vm.tfvars

• We will use machine_type = "e2-micro" from terraform.tfvars going forward.
• We have created other two files just to learn the multiple options available

  # vm.auto.tfvars
  # machine_type  = "e2-medium"
  
  # vm.tfvars
  # machine_type  = "e2-standard-2"
  

Step-09: Input Variables as Environment Variables (Unix or Linux Environments)

# Comment machine_type in terraform.tfvars
#machine_type  = "e2-micro"

# Set Environment Variable
export TF_VAR_machine_type="e2-standard-2"
echo $TF_VAR_machine_type

# Run Terraform Plan
terraform plan
Observation: Machine type configured will be "e2-standard-2" from environment variable set

# Unset Environment variable
unset TF_VAR_machine_type
echo $TF_VAR_machine_type

# Run Terraform Plan
terraform plan
Observation: Machine type configured will be "e2-small" from variables.tf default value

# Variable Precendence
Priority-1: Any -var and -var-file options on the command line, in the order they are provided. 
Priority-2: Any *.auto.tfvars or *.auto.tfvars.json files, processed in lexical order of their filenames.
Priority-3: The terraform.tfvars.json file, if present.
Priority-4: The terraform.tfvars file, if present.
Priority-5: Environment variables

# Comment machine_type in terraform.tfvars
machine_type  = "e2-micro"

Step-10: c6-output-values.tf - Define Output Values

• Output Values

  # Terraform Output Values
  ## ATTRIBUTES
  output "vm_instanceid" {
    description = "VM Instance ID"
    value = google_compute_instance.myapp1.instance_id
  }
  
  output "vm_selflink" {
    description = "VM Instance Self link"
    value = google_compute_instance.myapp1.self_link
  }
  
  output "vm_id" {
    description = "VM ID"
    value = google_compute_instance.myapp1.id
  }
  
  output "vm_external_ip" {
    description = "VM External IPs"
    value = google_compute_instance.myapp1.network_interface.0.access_config.0.nat_ip
  }
  
  ## ARGUMENTS
  output "vm_name" {
    description = "VM Name"
    value = google_compute_instance.myapp1.name
  }
  
  output "vm_machine_type" {
    description = "VM Machine Type"
    value = google_compute_instance.myapp1.machine_type
  }
  

Step-11: Execute Terraform Commands

# Terraform Initialize
terraform init
Observation:
1) Initialized Local Backend
2) Downloaded the provider plugins (initialized plugins)
3) Review the folder structure ".terraform folder"

# Terraform Validate
terraform validate
Observation:
1) If any changes to files, those will come as printed in stdout (those file names will be printed in CLI)

# Terraform Plan
terraform plan
1) Verify the number of resources that going to get created
2) Verify the variable replacements worked as expected

# Terraform Apply
terraform apply 
[or]
terraform apply -auto-approve
Observations:
1) Create resources on cloud
2) Created terraform.tfstate file when you run the terraform apply command

Step-12: Access Application

# Access index.html
http://<EXTERNAL-IP>/index.html
http://<EXTERNAL-IP>/app1/index.html

Step-13: Clean-Up

# Terraform Destroy
terraform plan -destroy  # You can view destroy plan using this command
terraform destroy

# Clean-Up Files
rm -rf .terraform*
rm -rf terraform.tfstate*

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