Getting started with Terraform

Terraform is a tool for building, changing, and versioning infrastructure safely and efficiently.

Install

You can see many options to install Terraform on your machine on this document

We choose chocolatey because is the easiest way.

choco install terraform

Syntax

variables (.tf)

If possible, all variables must be inside this file.

Terraform variable is defined on variables.tf file as:

variable "variable_name" {
    type            = string
    default         = "value"
}

The syntax for get any value from variables.tf is:

var.variable_name

Secrets can store here but it's not recommended because this file maybe will be store on control version system and any user can reveal the secret.

This secret (or any variable) can be replaced when apply command is executed as:

terraform apply -var="variable_name=value"

config (.tf)

On this file we can define different providers that we will use on our process.

provider "azurerm" {
  subscription_id = var.azure_subscription_id
  tenant_id       = var.azure_tenant_id
  client_id       = var.azure_client_id
  client_secret   = var.azure_client_secret
  features {}
}

Note: you can generate variables like client ID and client secret using this guide

main (.tf)

This file contains all resources that Terraform will create, update or delete on specific vendor infrastructure.

With Terraform you can create on Azure all services defined on this document.

For example, to create an App Service with related App Service Plan.

resource "azurerm_app_service_plan" "namespace" {
  name                    = "service_plan_name"
  location                = var.azure_location
  resource_group_name     = var.azure_resource_group
  kind                    = "Windows"
  sku {
    tier = "Free"
    size = "F1"
  }
  tags                    = var.azure_common_tags 
}

resource "azurerm_app_service" "namespace" {
  name                    = "app-service-name"
  resource_group_name     = var.azure_resource_group
  location                = var.azure_location  
  app_service_plan_id     = azurerm_app_service_plan.namespace.id
  tags                    = var.azure_common_tags
}

output (.tf)

Output values is a way to capture information from created or update resources

output "app_service_id" {
  value = azurerm_app_service.demo.id
}

output "app_service_default_site_hostname" {
  value = azurerm_app_service.demo.default_site_hostname
}

output "app_service_username" {
  value = azurerm_app_service.demo.site_credential[0].username
}

output "app_service_password" {
  value = azurerm_app_service.demo.site_credential[0].password
}

When Terraform executes successfully throught terraform apply command, it returns a set of data with resource information

app_service_id = /subscriptions/416268c2-d33e-4407-9e28-6db4446ae43f/resourceGroups/MyResourceGroup/providers/Microsoft.Web/sites/demo-terraform-app-service

app_service_default_site_hostname = demo-terraform-app-service.azurewebsites.net

app_service_username = $demo-terraform-app-service

app_service_password = veEHEMQdnhql7cxw0HyNSZzP6SRB8yq2cadvqdaw4Y6hRedX6wzzTl1DPzSc

To check, we can use this parameters to validate infrastructure creation

curl demo-terraform-app-service.azurewebsites.net

StatusCode        : 200
StatusDescription : OK
...

Main commands

The complete list of Terraform commands is available here

init

Initialize a working directory containing Terraform configuration files

terraform init

validate

Validates configuration without accessing any remote services

terraform validate

terraform validate --json

An example of successful validation

Success! The configuration is valid.

{
  "valid": true,
  "error_count": 0,
  "warning_count": 0,
  "diagnostics": []
}

An example of failed validation

Error: Invalid expression

  on main.tf line 3, in resource "azurerm_app_service_plan" "terraformdemo":
   3:   location                = #var.azure_location
   4:

Expected the start of an expression, but found an invalid expression token.

{
  "valid": false,
  "error_count": 1,
  "warning_count": 0,
  "diagnostics": [
    {
      "severity": "error",
      "summary": "Invalid expression",
      "detail": "Expected the start of an expression, but found an invalid expression token.",
      "range": {
        "filename": "main.tf",
        "start": {
          "line": 3,
          "column": 29,
          "byte": 142
        },
        "end": {
          "line": 4,
          "column": 1,
          "byte": 164
        }
      }
    }
  ]
}

apply

Applies the changes required to reach the desired state of the configuration. This means that Terraform can create, update or remove resources.

terraform apply

destroy

Remove all resources managed by Terraform.

terraform destroy

📘 Demos

On this document you can see the prepared demos.

Contact

You can contact me via Twitter @sergiobarriel