Configure Terraform

To use Terraform in your Google Distributed Cloud (GDC) air-gapped environment, you must download it and configure it to handle Kubernetes resources.

Before you begin

Download Terraform to your workstation following the documentation provided by HashiCorp: https://developer.hashicorp.com/terraform/install.
Verify you have an existing GDC storage bucket. If you don't have a storage bucket, create one.
Make sure your system can recognize the Certificate Authority (CA) certificate used by object storage.

Manage the state file

The state file in Terraform is used to record the current state of the deployment and map it to the Terraform configuration. Since GDC object storage is implemented using S3, you can use the Terraform S3 API to sync with a shared state file. To do this, you must configure Terraform to sync with the remote state:

Add the following configuration to a Terraform file that is stored locally, such as the main.tf file:
```
terraform {
  backend "s3" {
    bucket = "BUCKET_FQN"
    key = "TF_STATE_PATH"
    endpoint = "BUCKET_ENDPOINT"
    skip_credentials_validation = true
    force_path_style = true
    access_key = "ACCESS_KEY"
    secret_key = "SECRET_KEY"
    ...
  }
}
```
Replace the following:
- BUCKET_FQN: the fully qualified name from the Bucket custom resource.
- TF_STATE_PATH: the location of the Terraform state file to store in the storage bucket.
- BUCKET_ENDPOINT: the endpoint from the Bucket custom resource.
- ACCESS_KEY: the access key acquired from the secret containing your access credentials. Follow Obtain bucket access credentials to acquire the access key.
- SECRET_KEY: the secret key acquired from the secret containing your access credentials. Follow Obtain bucket access credentials to acquire the secret key.
You must set skip_credentials_validation and force_style_path to true since GDC does not support the credential validation and uses the path style endpoint.

Note: We recommend using environment variables to store the credentials. If credentials are hardcoded, they are stored within the .terraform directory and in plan files.
Initialize the new state file edits in the storage bucket you specified in the previous step:
```
terraform init
```
Terraform might ask for an AWS region as a required input, but the value is not used since you're using GDC object storage. Input any AWS region to satisfy the requirement.

Set permissions

Besides the permissions required to perform a specific task using Terraform, such as creating a GDC project, you must also have permissions to view custom resource definitions at that scope. Apply the required permissions to use Terraform:

Create the crd-viewer cluster role resource:
```
kubectl apply --kubeconfig KUBECONFIG -f - <<EOF
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: crd-viewer
rules:
- apiGroups: ["apiextensions.k8s.io"]
  resources: ["customresourcedefinitions"]
  verbs: ["get", "list", "watch"]
EOF
```
Replace KUBECONFIG with the kubeconfig file of the API server or cluster that hosts the resource you're managing with Terraform. For example, most resources run on the Management API server. For container workloads, set your Kubernetes cluster kubeconfig file. Be sure to set the global API server if you're managing a global resource.

Bind the cluster role defined in the previous step to the user:

kubectl apply --kubeconfig KUBECONFIG -f - <<EOF
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: crd-viewer-binding
subjects:
- kind: User
  name: USER_EMAIL
roleRef:
  kind: ClusterRole
  name: crd-viewer
  apiGroup: rbac.authorization.k8s.io
EOF

Repeat these steps for each API server or cluster you want to set Terraform permissions for.

Install and configure Terraform provider

You must install the Kubernetes Provider to provision and manage Kubernetes resources.

In a Terraform file within your module, such as the main.tf file, insert the following required_providers block:

terraform {
  required_providers {
    kubernetes = {
      source = "hashicorp/kubernetes"
      version = "~>2.6.1"
    }
  }
}

Initialize your Terraform working directory to install the provider:
```
terraform init
```