How you can provision GCP infrastructure including IAM, VPC, GCS, and VMs using Terraform with a modular approach and multiple environment support (dev, pre-prod, prod), along with automated deployment using GitHub Actions with authentication and authorization

Directory Structure

terraform/
├── modules/
│   ├── iam/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   └── outputs.tf
│   ├── vpc/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   └── outputs.tf
│   ├── gcs/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   └── outputs.tf
│   └── vm/
│       ├── main.tf
│       ├── variables.tf
│       └── outputs.tf
├── environments/
│   ├── dev/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   ├── backend.tf
│   │   └── terraform.tfvars
│   ├── preprod/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   ├── backend.tf
│   │   └── terraform.tfvars
│   └── prod/
│       ├── main.tf
│       ├── variables.tf
│       ├── backend.tf
│       └── terraform.tfvars
├── .github/
│   └── workflows/
│       └── terraform.yml
└── README.md

Modules

1. IAM Module (modules/iam/): Manages IAM roles and permissions.
2. VPC Module (modules/vpc/): Creates a VPC network and subnets.
3. GCS Module (modules/gcs/): Sets up Google Cloud Storage buckets.
4. VM Module (modules/vm/): Provisions virtual machines.

Environments

Each environment (dev, preprod, prod) has its own Terraform configuration files:

1. Terraform Files (environments/{env}/):

• main.tf: Defines the infrastructure resources using modules.
• variables.tf: Declares environment-specific variables.
• backend.tf: Configures Terraform backend for state storage.
• terraform.tfvars: Specifies environment-specific values for variables.

GitHub Actions

1. Terraform Workflow (.github/workflows/terraform.yml):

• Triggers on push to specific branches (e.g., dev, preprod, prod).
• Authenticates with Google Cloud using service account key.
• Deploys Terraform configurations for the corresponding environment.

Example Terraform Configuration

Let’s take the dev environment as an example:

environments/dev/main.tf

provider "google" {
  project = var.project_id
  region  = var.region
}

module "iam" {
  source          = "../../modules/iam"
  project_id      = var.project_id
  dev_iam_members = var.dev_iam_members
}

module "vpc" {
  source          = "../../modules/vpc"
  project_id      = var.project_id
  region          = var.region
  dev_subnet_cidr = var.dev_subnet_cidr
}

module "gcs" {
  source     = "../../modules/gcs"
  project_id = var.project_id
  bucket_name = var.dev_bucket_name
}

module "vm" {
  source         = "../../modules/vm"
  project_id     = var.project_id
  region         = var.region
  zone           = var.zone
  instance_count = var.dev_instance_count
}

environments/dev/variables.tf

variable "project_id" {
  description = "Google Cloud Project ID"
}

variable "region" {
  description = "GCP region"
}

variable "zone" {
  description = "GCP zone"
}

variable "dev_iam_members" {
  description = "IAM members for dev environment"
}

variable "dev_subnet_cidr" {
  description = "CIDR block for dev subnet"
}

variable "dev_bucket_name" {
  description = "GCS bucket name for dev environment"
}

variable "dev_instance_count" {
  description = "Number of VM instances for dev environment"
}

.github/workflows/terraform.yml

name: Terraform

on:
  push:
    branches:
      - main
      - dev
  pull_request:
    branches:
      - main
      - dev

jobs:
  terraform:
    name: Terraform
    runs-on: ubuntu-latest
    env:
      TF_VERSION: 1.0.0
      TF_WORKING_DIR: ./path/to/your/terraform/files
      GOOGLE_APPLICATION_CREDENTIALS: ${{ secrets.GCP_SA_KEY }}

    steps:
      - name: Checkout repository
        uses: actions/checkout@v2

      - name: Setup Terraform
        uses: hashicorp/setup-terraform@v1
        with:
          terraform_version: ${{ env.TF_VERSION }}

      - name: Terraform Init
        working-directory: ${{ env.TF_WORKING_DIR }}
        run: terraform init

      - name: Terraform Plan
        working-directory: ${{ env.TF_WORKING_DIR }}
        run: terraform plan

      - name: Terraform Apply
        working-directory: ${{ env.TF_WORKING_DIR }}
        run: terraform apply -auto-approve -var-file=environments/${{ github.ref_name }}/terraform.tfvars

Additional Notes:

• Make sure to define the environment-specific variable files (terraform.tfvars) in each environment directory (environments/dev/terraform.tfvars, environments/preprod/terraform.tfvars, environments/prod/terraform.tfvars).
• Ensure your Terraform directory structure matches the path specified in TF_WORKING_DIR.

GitHub Actions workflow should correctly initialize, plan, and apply Terraform configurations for different environments based on the branch being pushed or the pull request target.