task_003_vars_and_resource_dependencies

Creating Resource Dependencies with Terraform

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Select - DevOps Engineer, SRE Learning Path

High Level Objectives

• Use variables and output values
• Observe implicit dependency
• Create explicit resource dependency
• View Dependency Graph

Skills

• variables
• output values
• explicit resource dependency
• dependency graph
• terraform

Version Stack

Stack	Version
Terraform	1.3.6

Initialize Terraform

terraform -version

# Create a directory for your Terraform configuration and navigate to it by running the following command:
mkdir tfinfra && cd $_

touch provider.tf

• provider.tf

# Get project ID
gcloud config list --format 'value(core.project)'

  provider "google" {
  project = "<your-project-id>"
  region  = "us-east1"
  zone    = "us-east1-b"
}

• Initialize

terraform init

View Implicit Resource Dependency

touch instance.tf

• instance.tf

resource google_compute_instance "vm_instance" {
name         = "${var.instance_name}"
zone         = "${var.instance_zone}"
machine_type = "${var.instance_type}"
boot_disk {
    initialize_params {
      image = "debian-cloud/debian-10"
      }
  }
 network_interface {
    network = "default"
    access_config {
      # Allocate a one-to-one NAT IP to the instance
    }
  }
}

touch variables.tf

• variables.tf

variable "instance_name" {
  type        = string
  description = "Name for the Google Compute instance"
}
variable "instance_zone" {
  type        = string
  description = "Zone for the Google Compute instance"
}
variable "instance_type" {
  type        = string
  description = "Disk type of the Google Compute instance"
  default     = "n1-standard-1"
  }

touch outputs.tf

• outputs.tf

output "network_IP" {
  value = google_compute_instance.vm_instance.instance_id
  description = "The internal ip address of the instance"
}
output "instance_link" {
  value = google_compute_instance.vm_instance.self_link
  description = "The URI of the created resource."
}

• Let's assign static IP to VM instance

• Append to instance.tf

resource "google_compute_address" "vm_static_ip" {
  name = "terraform-static-ip"
}

• Update the network_interface configuration for your instance like so:

 network_interface {
    network = "default"
    access_config {
      # Allocate a one-to-one NAT IP to the instance
      nat_ip = google_compute_address.vm_static_ip.address
    }
  }

• Init, Plan, Apply

terraform init

# var.instance_name: myinstance
# var.instance_zone: us-east1-b
terraform plan

# var.instance_name: myinstance
# var.instance_zone: us-east1-b
terraform apply

• Verify on Cloud Console

Create Explicit Dependency

touch exp.tf

• exp.tf

resource "google_compute_instance" "another_instance" {
  name         = "terraform-instance-2"
  machine_type = "f1-micro"
  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-10"
    }
  }
  network_interface {
    network = "default"
    access_config {
    }
  }
  # Tells Terraform that this VM instance must be created only after the
  # storage bucket has been created.
  depends_on = [google_storage_bucket.example_bucket]
}
resource "google_storage_bucket" "example_bucket" {
  name     = "<UNIQUE-BUCKET-NAME>"
  location = "US"
  website {
    main_page_suffix = "index.html"
    not_found_page   = "404.html"
  }
}

• Init, Plan, Apply

terraform init

# var.instance_name: myinstance
# var.instance_zone: us-east1-b
terraform plan

# var.instance_name: myinstance
# var.instance_zone: us-east1-b
terraform apply

• Validate on console

View Dependency Graph

terraform graph | dot -Tsvg > graph.svg