broken data azurerm_subnet route_table_id: not functioning

[bernadinm]

Terraform Version

$ terraform -v
Terraform v0.11.7
+ provider.azurerm v1.5.0

Affected Resource(s)

data "azurerm_subnet" "public" {
  name                 = "cisco-csr-subnet-public"
  virtual_network_name = "${data.azurerm_virtual_network.current.name}"
  resource_group_name  = "${data.azurerm_resource_group.rg.name}"
  route_table_id       = "${azurerm_route_table.RTPublic.id}" # Not functioning 
}

Debug Output

Error: data.azurerm_subnet.public: "route_table_id": this field cannot be set

Panic Output

Expected Behavior

I expected that an existing subnet will be associated with an existing routing table.

Actual Behavior

Terraform failed.

Steps to Reproduce

1. terraform apply

Important Factoids

There does not see to be any other way to do this in terraform. The data resource is the most appropriate resource to achieve linking an existing subnet to a routing table. Currently it is possible within the Azure Portal UI to associate the subnet to the routing table, but not with terraform at the moment.

[tombuildsstuff]

hi @bernadinm

Thanks for opening this issue, apologies for the delayed response here!

Data Sources in Terraform are for referencing information about existing resources (e.g. getting the ID of a Storage Account) - rather than for modifying information about them.

It's possible to import an existing resource into Terraform using theterraform import command - which can then be managed via the azurerm_route_table Resource. for instance here's how to import a Route Table into the State:

terraform import azurerm_route_table.test /subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/mygroup1/providers/Microsoft.Network/routeTables/mytable1

Once the existing Resource has been imported into Terraform, it's then possible to change the value of this property via the azurerm_route_table resource. Would you be able to take a look and see if this resolves your issue?

Since this is a question about Terraform rather than a bug in Terraform - I'm going to close this issue for the moment (but we'll continue to take a look/respond 😄)

Thanks!

[bernadinm]

Thank you @tombuildsstuff, if this is the case then what we're missing is this resource here route_table_association in the same way we have it for AWS.

https://www.terraform.io/docs/providers/aws/r/route_table_association.html

Do you recommend me making a separate feature request to ask for this resource in terraform-provider-azurerm provider?

data "azurerm_subnet" "public" {
  name                 = "mysubnet"
  virtual_network_name = "some-resource-group"
}

data "azurerm_route_table" "test" {
  name                = "myroutetable"
  resource_group_name = "some-resource-group"
}

resource "azurerm_route_table_association" "a" {
  subnet_id      = "${data.azurerm_subnet.public.id}"
  route_table_id = "${data.azurerm_route_table.test.id}"
}

[tombuildsstuff]

hi @bernadinm

Unfortunately the Azure API isn't designed in such a way that this is possible (in general the API generally prefers creating monolithic resources rather than composable resources) - whilst it technically is possible to implement this resource by hacking around the azurerm_subnet resource, it'd lead to us having conflicts with that resource; as such the only way we could implement this safely would be to deprecate the field route_table_id from the subnet resource in favour of this new resource.

That said - I think this could make sense as a change but needs some more thought; would you mind opening a new issue specifically about this?

Thanks!

[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!