Terraform

Infrastructure as code is the idea of defining everything you need to build in a programming language like Terraform (or Ansible etc.) and then use that code to stand up your infrastructure.

Why infrastructure as code?

• Helps you maintain an audit trail of every single change that goes into your environment.
• Steps are defined as code, eliminating human intervention and in turn human errors.
• You can test your code by building automated pipelines that will stand up your infrastructure and run tests against it.
• Can sync up Dev, Staging and production. Ideally all the enviroments should mirror each other to ensure the programs/scripts run seamlessly.
• You can easily re-build your infrastructure in case of failure. Imagine spinning up 12 different VMs, 2 storages etc. manually.

Terraform Basics

Terraform maintains the set of instructions in Terraform configuration files. They end with .tf extensions.

Let's consider the following file for our example -

terraform {
  required_providers {
    google = {
      source = "hashicorp/google"
      version = "3.5.0"
    }
  }
}

provider "google" {
  credentials = file("<NAME>.json")

  project = "<PROJECT_ID>"
  region  = "us-central1"
  zone    = "us-central1-c"
}

resource "google_compute_network" "vpc_network" {
  name = "terraform-network"
}

Terraform divides information into blocks, defined in curly braces {}. There are three main blocks - terraform, provider, resource.

Terraform Block

The terraform {} block contains Terraform settings, including the required providers Terraform will use to provision your infrastructure.

terraform {
  required_providers {
    google = {
      source = "hashicorp/google"
      version = "3.5.0"
    }
  }
}

For each provider, the source attribute defines an optional hostname, a namespace, and the provider type. Terraform installs providers from the Terraform Registry by default. In this example configuration, the google provider's source is defined as hashicorp/google, which is shorthand for registry.terraform.io/hashicorp/google.

You can also define a version constraint for each provider in the required_providers block. The version attribute is optional.

Providers

The provider block configures the specified provider, in this case google. A provider is a plugin that Terraform uses to create and manage your resources. You can define multiple provider blocks in a Terraform configuration to manage resources from different providers.

provider "google" {
  credentials = file("<NAME>.json")

  project = "<PROJECT_ID>"
  region  = "us-central1"
  zone    = "us-central1-c"
}

Resource

The resource block is used to define components of your infrastructure. A resource might be -

• A physical component like a server
• A logical component like a Heroku Application

Resource blocks have two strings before the block -

• Resource type
• Resource name

resource "google_compute_network" "vpc_network" {
  name = "terraform-network"
}

In this example, the resource type is google_compute_network and the resource name is vpc_network. Together the resource type and the resource name provide and unique ID for the resource google_compute_network.vpc_network. The ID must be unique within the module.

The prefix of the type maps to the name of the provider. In this example, terraform manages the google_compute_network with the google provider. compute indicates the GCP product family and instance is the resource name.

The resource name is used to refer to the resource from elsewhere in the same Terraform module, but has no significance outside that module's scope.

Inspect State

Terraform stores the IDs and properties of the resources it manages in the terraform.tfstate file, so that it can update or destroy those resources going forward.
The Terraform state file is the only way Terraform can track which resources it manages, and often contains sensitive information.

Input Variables

To make your configuration more dynamic and flexible you can include variables. If a default value is set, then the variable becomes optional. Else it is a required variable.

variable "project" { }

variable "region" {
  default = "us-central1"
}

variable "zone" {
  default = "us-central1-c"
}

You can populate variables using command line or via a file. Terraform automatically loads files called terraform.tfvars or matching *.auto.tfvars in the working directory when running operations.

Terraform Commands

Intialize the directory and download the necessary plugins and provider details:

terraform init

Format your configuration files:

terraform fmt

Validate your configuration files for syntax and internal consistency:

terraform validate

Create and display apply plan:

terraform plan

Apply the changes to your infrastructure:

terraform apply

Inspect the current state:

terraform show

Terminate resources:

terraform destroy