terraform-default-behaviours-examples.md

Terraform configurations ranging from implicit to (more) explicit

Directory contents

For all the below, the directory before running terraform init contains only main.tf

my-terraform-project/
├─ main.tf

Config #1 : Using all the default behaviours

This is sufficient as a Terraform config for GCP, assuming you're supplying some environment variables:

• Authentication, e.g. via a GOOGLE_CREDENTIALS environment variable.
• Default values used for provisioning resources : GOOGLE_PROJECT, GOOGLE_REGION, GOOGLE_ZONE environment variables

# main.tf

resource "google_storage_bucket" "my-bucket" {
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
      age = 3
    }
    action {
      type = "Delete"
    }
  }

Config #2 : Avoid defaulting to latest version of provider (adding version constraints)

# main.tf

terraform {
    required_providers {
        google = {
            version = "~>4.1.0"
        }
    }
}

resource "google_storage_bucket" "my-bucket" {
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
      age = 3
    }
    action {
      type = "Delete"
    }
  }

Config #3: Avoid default of looking for the preferred local name (explicitly deciding how Terraform chooses which provider to use for a resource)

# main.tf

terraform {
    required_providers {
        # The official Google provider is using the preferred local name here
        # We could change it to hashicorp-google, but then all resources will need a provider meta-argument
        google = {
            source = hashicorp/google
            version = "~>4.1.0"
        }
        my-org-google = {
            source = my-org/google
            version = "=1.3.0"
        }
    }
}

resource "google_storage_bucket" "my-bucket" {
  # No provider argument needed here
  # We are knowingly using Terraform's default behaviour to look for a provider with a local name matching
  # the first word in the resource type at the top of this resource block
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
      age = 3
    }
    action {
      type = "Delete"
    }
}

resource "google_storage_bucket" "bucket-made-with-my-provider" {
  provider      = my-org-google # local name from `required_providers` block 
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
    age = 3
    }
    action {
      type = "Delete"
    }
}

Config #3.5 : Exploring the concept of alias versus local name

# main.tf

terraform {
    required_providers {
        google = {
            source = hashicorp/google
            version = "~>4.1.0"
        }
        my-org-google = {
            source = my-org/google
            version = "=1.3.0"
        }
    }
}

# This is the default provider configuration
provider "google" {
  project     = "my-project-id"
  region      = "us-central1"
  zone        = "us-central1-c"
}

provider "google" {
  alias       = "europe" # alias needed!
  project     = "my-project-id"
  region      = "europe-west2"
  zone        = "europe-west2-a"
}

resource "google_storage_bucket" "my-US-bucket" {
  # No provider argument needed here
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
      age = 3
    }
    action {
      type = "Delete"
    }
}

resource "google_storage_bucket" "my-EU-bucket" {
  provider      = google.europe # <local name>.<alias>
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
      age = 3
    }
    action {
      type = "Delete"
    }
}

resource "google_storage_bucket" "bucket-made-with-my-provider" {
  provider      = my-org-google
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
    age = 3
    }
    action {
      type = "Delete"
    }
}

Config #4 : Avoiding using the public Registry by default (setting the hostname in registry source address)

Note: the config below requires the terraform CLI to be configured with credentials to access the specific private registry.

There's a section in the documentation describing how to configure credentials for the CLI here.

# main.tf

terraform {
    required_providers {
        # The official Google provider is using the preferred local name here
        # We could change it to hashicorp-google, but then all resources will need a `provider` meta-argument
        google = {
            source = hashicorp/google
            version = "~>4.1.0"
        }
        my-org-google = {
            source = "app.terraform.io/my-org/google" # Using a private Registry hosted in Terraform Cloud
            version = "=1.3.0"
        }
    }
}

# This is the default provider configuration
provider "google" {
  project     = "my-project-id"
  region      = "us-central1"
  zone        = "us-central1-c"
}

provider "google" {
  alias       = "europe" # alias needed!
  project     = "my-project-id"
  region      = "europe-west2"
  zone        = "europe-west2-a"
}

resource "google_storage_bucket" "my-US-bucket" {
  # No provider argument needed here
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
      age = 3
    }
    action {
      type = "Delete"
    }
}

resource "google_storage_bucket" "my-EU-bucket" {
  provider      = google.europe
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
      age = 3
    }
    action {
      type = "Delete"
    }
}

resource "google_storage_bucket" "bucket-made-with-my-provider" {
  provider      = my-org-google
  name          = "auto-expiring-bucket"
  location      = "US"
  force_destroy = true

  lifecycle_rule {
    condition {
    age = 3
    }
    action {
      type = "Delete"
    }
}