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[/tʃiːt/] To act dishonestly or unfairly in order to gain an advantage.

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Key features

Tool for building/changing/versioning infrastructure, can manage both low-level components such as compute instances, storage, and networking, and high-level components such as DNS entries and SaaS features.
Uses a language called HCL - HashiCorp Configuration Language.
Terraform uses plugins called providers to interface with the resources in the cloud provider.

Terraform state

By default is stored in terraform.tfstate file or it can be stored remotely e.g. Azure VM

# main.tf file
# store state remotely in Azure VM
terraform {
    backend "azurerm" {
        resource_group_name = "RG_NAME"
        storage_account_name = "STORAGE_ACCOUNT_NAME"
        container_name = "tfstate"
        key = "terraform.tfstate"
    }

    required_version = ">= 0.13"
    required_providers {
    azurerm = {
      source = "hashicorp/azurerm"
      version = "2.49.0"
    }
  }
}

Terraform backend used to define the state data files:
- By default, Terraform uses a backend called local, which stores state as a local file on disk
- You can configure the backend by adding the backend block to your configuration, e.g remote backend:

  terraform {
  backend "remote" {
    organization = "example_corp"

    workspaces {
      name = "my-app-prod"
    }
  }

Terraform state represents the current state of your infrastructure, while the Terraform backend determines where and how this state is stored and accessed.
Terraform flow:

terraform init # initialize a working directory containing the Terraform configuration files, it  will create .terraform.lock.hcl to record the provider selections it made above

# validate if the configuration is correct
terraform validate

terraform plan # present you the difference between reality at a given time and config you intend to apply
terraform plan -out maint.tfplan # creates an execution plan to a specified output file

terraform apply # apply the changes required to reach the desired state of the configuration.
terraform apply main.tfplan # apply the plan from file e.g. maint.tfplan

# proposed destroy changes without executing them
terraform plan -destroy -out main.destroy.tfplan
terraform apply main.destroy.tfplan

The init command must be called:
- On any new environment that configures a backend
- On any change of the backend configuration (including the type of backend)
- On removing backend configuration completely

Configuration files

1) Provider block to configure the named provider (multiple providers can exists):

maint.tf

# provider block

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


provider "google" {
  version = "3.5.0"

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

#compute instance resource

resource "google_compute_instance" "vm_instance" {
  name         = "terraform-instance"
  machine_type = "f1-micro"

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-9"
    }
  }

  network_interface {
    network = google_compute_network.vpc_network.name
    access_config {
    }
  }
}

Action

If you have a resourge e.g. ResourceGroup create manually in Azure_portal in order to use it you must import it:

# imported the resource group which was created manually
terraform import azurerm_resource_group.<RG_NAME_LOWERCASE> /subscriptions/<SUBS_ID>/resourceGroups/<RG_NAME>

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                   \/________/         @dejanualex