azurerm_application_gateway doesn't allow empty backend IP list

[simonbrady]

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Terraform (and AzureRM Provider) Version

Terraform v0.13.0
+ provider registry.terraform.io/hashicorp/azurerm v2.24.0

Affected Resource(s)

• azurerm_application_gateway

Terraform Configuration Files

https://gist.github.com/simonbrady/ac018ec5302c7969a4b5baa08a711a66#file-main-tf

Debug Output

https://gist.github.com/simonbrady/ac018ec5302c7969a4b5baa08a711a66#file-trace-log

Panic Output

n/a

Expected Behavior

Terraform creates an application gateway with an empty backend pool

Actual Behavior

Plan fails with

Error: backend_address_pool.0.ip_addresses: attribute supports 1 item as a minimum, config has 0 declared

Steps to Reproduce

1. terraform apply

Important Factoids

This breaks a real-world use case, where a customer wants to use the same code to deploy app gateways in Prod and DR but not create any VMs in DR since that's handled by ASR failover. Since ip_addresses is an optional attribute, the workaround is to write

ip_addresses = (var.vm_count > 0 ? azurerm_network_interface.vm[*].private_ip_address : null)

which is an ugly hack.

References

[simonbrady]

Fix in #8210

[ghost]

This has been released in version 2.25.0 of the provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading. As an example:

provider "azurerm" {
    version = "~> 2.25.0"
}
# ... other configuration ...

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. If you feel I made an error 🤖 🙉 , please reach out to my human friends 👉 [email protected]. Thanks!