terraform-provider-azurerm fails to identify dependencies

[juanjojulian]

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Terraform (and AzureRM Provider) Version

Terraform v0.11.11

• provider.azurerm v1.20.0

Affected Resource(s)

*azurerm_public_ip
*azurerm_resource_group

Terraform Configuration Files

resource "azurerm_resource_group" "main" {
  name     = "${var.sub-name}-${var.region}-${var.aplication}-rg"
  location = "${var.region}"
}

resource "azurerm_public_ip" "main" {
  count                = "${var.public_ip == "true" ? 1 : 0}"
  name                 = "${var.sub-name}-${var.region}-${var.hostname}-PublicIP${count.index}"
  location             = "${var.region}"
  resource_group_name  = "${var.sub-name}-${var.region}-${var.aplication}-rg"
  public_ip_address_allocation = "${var.public_ip_alloc}"
}

Expected Behavior

Terraform should understand that the resource group should be created prior to attempting the public ip creation.

Actual Behavior

Error: Error applying plan:

1 error(s) occurred:

* module.XXX.azurerm_public_ip.main: 1 error(s) occurred:

* azurerm_public_ip.main: Error Creating/Updating Public IP "XXX-PublicIP0" (Resource Group "XXX-rg"): network.PublicIPAddressesClient#CreateOrUpdate: Failure sending request: StatusCode=0 -- Original Error: Code="ResourceGroupNotFound" Message="Resource group 'XXX-rg' could not be found."

###NOTE
This problem is solved using depends_on = ["azurerm_resource_group.main"] but as per Terraform documentation this should not be necessary as Terraform should solve all dependencies.

[tombuildsstuff]

hey @juanjojulian

Thanks for opening this issue :)

Terraform infers the dependencies between resources in one of two ways - ether using an Implicit Dependency or using an Explicit Dependency.

We'd recommend using an Implicit Dependency where possible - which is where you use the Interpolation Syntax to reference between resources, for example:

resource "azurerm_resource_group" "main" {
  name     = "example-resource-group"
  location = "West Europe"
}
resource "azurerm_public_ip" "main" {
  name                 = "my-example-public-ip"
  location             = "${azurerm_resource_group.main.location}"
  resource_group_name  = "${azurerm_resource_group.main.name}"
  public_ip_address_allocation = "Dynamic"
}

The other approach would be to use an Explicit Dependency which can be achieved using the depends_on parameter - but we'd recommend using an Implicit Dependency where possible (since it means you don't need to keep this extra parameter up to date). Without the dependency information (either an Implicit or Explicit Dependency) Terraform doesn't know these resources rely on one another - which means it believes it can create them in parallel (which is why you're seeing this error about the Resource Group not existing).

Would you be able to take a look and see if using an Implicit Dependency works for you? Since this is a question about Terraform Configuration rather than a bug in Terraform, I'm going to close this issue for the moment (but we'll continue responding 😄)

Thanks!

[juanjojulian]

Thanks Tom, I will try using interpolation syntax :-)

[ghost]

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