Terraform

Terraform automates the deployment of infrastructure through Infrastructure as Code (IaC), creating and managing components across various providers via an abstraction layer.

gcp_cicd_bootstrap: Branch with complete Terraform Cloud CI/CD bootstrap config w/ Github actions and Google Cloud Build

Key Concepts:

Terraform CLI: The command-line interface tool that allows users to execute Terraform commands.
Providers: Plugins for managing resources with cloud providers like AWS, Azure, Google Cloud, Docker, Kubernetes, etc.
Resources: Individual infrastructure components, such as virtual machines, network interfaces, or managed databases.
Variables: Parameters that dynamically configure resources, allowing for flexibility and reusability of configurations.
Inputs (Input Variables): Parameters defined by users to customize Terraform configurations, allowing users to input custom values without altering the main configuration.
Functions: Built-in functions allow for basic transformations and computations within Terraform configuration.
Expressions: Used to reference or compute values within a configuration, enabling dynamic configurations.
Modules: Reusable blocks of configuration, grouping related resources, to simplify setup and management.
Outputs (Output Variables): Variables that provide information about the infrastructure, useful for referencing in other configurations or modules.
State: Tracks the current state of your infrastructure, comparing it to the planned state to determine changes.
Remote State (Back-end): Stores the state file in a remote data store, facilitating team collaboration and state management.
Declarative Syntax: You specify the desired end-state of the infrastructure, and Terraform figures out the steps to achieve it.
Idempotency: Ensures operations produce the same outcome, regardless of how many times they are executed.
Terraform Plan: Generates an execution plan, showing what Terraform will do when you apply your configuration.
Terraform Apply: Executes the actions proposed in a Terraform plan to reach the desired state of the configuration.
Terraform Workspace: Allows for the management of multiple distinct sets of infrastructure resources or environments from the same configuration.

Using Terraform (HCL - HashiCorp Configuration Language):

Initialization: Prepares your directory for Terraform operations, including downloading required providers.
```
terraform init
```
Validation: Checks if the configuration is syntactically valid and internally consistent.
```
terraform validate
```
Formatting: Adjusts the configuration files to Terraform's standard formatting style.
```
terraform fmt
```
Planning: Creates an execution plan, showing what Terraform intends to do to achieve the desired infrastructure state.
```
terraform plan
```
Applying: Executes the actions proposed in the Terraform plan to reach the desired state.
```
terraform apply
```
Destruction: Removes all resources defined in the Terraform configuration.
```
terraform destroy
```

Variables and Configuration:

Variables can be defined directly in .tf files or externalized into terraform.tfvars files, especially for sensitive data.
The configuration can be applied with the -var or -var-file flags during the apply step.

Getting Started:

Requirements:

AWS Bucket for .tfstate storage (e.g., <name>-terraform-bucket).
Configure aws.tfvars or gcloud.tfvars with provider-specific config variables like access_key, secret_key, region.

Initialization:

terraform init -var-file=aws.tfvars
terraform init -var-file=gcloud.tfvars

Apply Configuration:

terraform apply -var-file=aws.tfvars --auto-approve
terraform apply -var-file=gcloud.tfvars --auto-approve

Clean Up:

terraform destroy -var-file=aws.tfvars --auto-approve
terraform destroy -var-file=gcloud.tfvars --auto-approve

Kubernetes Configuration:

AWS EKS:

aws eks update-kubeconfig --name <your-cluster-name>

Google Cloud GKE:

gcloud container clusters get-credentials <name>-cluster --region us-central1 --project <project-name>

Code Formatting:

Ensure consistent formatting across all Terraform files.
```
terraform fmt -recursive
```

Google Cloud and Terraform: Tools and Setup

GCloud SDK: Necessary for authenticating and configuring GCP for use with Terraform.

Authenticate with GCP:

gcloud auth application-default login
gcloud auth login `ACCOUNT`
gcloud config set project <project-id>

Enable required GCP services:

gcloud services enable iam.googleapis.com
gcloud services enable cloudresourcemanager.googleapis.com

Deploying the Terraform Configuration

Generating an execution plan and applying it:

terraform plan -out=s1.tfplan
terraform apply s1.tfplan

For a visual representation of your Terraform plan:
```
terraform graph // Use with webgraphviz.com
```

Inspecting a plan:

terraform show s1.tfplan
terraform show -json s1.tfplan

Destroying Resources

Terraform Destroy: To remove all resources managed by Terraform.
```
terraform destroy
```
Alternatively, resources can be deleted directly in the GCP console.

Input Variables

Validate configurations with terraform validate.
Variables can be set via:
1. terraform.tfvars files.
2. CLI using -var or -var-file.
3. Environment variables.

Deploying a Remote State Configuration

Configure backend for state management:

terraform init -backend-config="bucket=remotestate_<project-id>"

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