Is there a way to refer to nested variable in Terraform script?

Question

I have a terraform script, which tries to refer to the attribute in the same resource. I need to pass "azurerm_container_group.aci_caddy.fqdn" to the container instance inside the container group.

resource "azurerm_container_group" "aci_caddy" {
  resource_group_name = "aci_caddy"
  location            = local.location
  name                = "aci_caddy"
  os_type             = "Linux"
  dns_name_label      = "aci-caddykang"

  container {
    name   = "app"
    image  = "apptest:latest"
    cpu    = "0.5"
    memory = "0.5"
    
    environment_variables = {
      SITE_ADDRESS = "${azurerm_container_group.aci_caddy.fqdn}"
    }

  }
}

but, I got the error message.

│ Error: Self-referential block
│ 
│   on aci-caddy-main.tf line 29, in resource "azurerm_container_group" "aci_caddy":
│   29:       SITE_ADDRESS = "${azurerm_container_group.aci_caddy.fqdn}"
│ 
│ Configuration for azurerm_container_group.aci_caddy may not refer to itself.

Is there a way to accomplish it? Thanks.

Answer 1

you should be able to export SITE_ADDRESS using your dns_name_label. So, instead of hardcoding dns_name_label. You can create a variable in Terraform

variable "dns_label" {
type = string
}

And then refer to this variable in your container group resource.

resource "azurerm_container_group" "aci_caddy" {
  resource_group_name = "aci_caddy"
  location            = local.location
  name                = "aci_caddy"
  os_type             = "Linux"
  dns_name_label      = var.dns_label

  container {
    name   = "app"
    image  = "apptest:latest"
    cpu    = "0.5"
    memory = "0.5"
    
    environment_variables = {
      SITE_ADDRESS = "${var.dns_label}-westus.azurecontainer.io"
    }

  }
}

If you want to further improve this, you can figure out how you can get the region/location from a azurerm provider data source. I am not exposed to azure provider, so couldn't find this quickly. But I know for a fact that FQDN is derived using your dns_name_label and .azurecontainer.io.