Terraform Conditional depending if a resource has been created

Question

I have created a compute module that has a conditional to create an external IP.

resource "google_compute_address" "external" {     
    count = "${var.EXT_IP_CREATE ? 1 : 0}"     
    name = "${var.NAME}-ext-ip"     
    address_type = "EXTERNAL"     
    region = "${var.REGION}"}

Within the compute instance resource block, I have the following network interface configuration:

network_interface {     
    network= "${var.NETWORK}"     
    network_ip = "${google_compute_address.internal.address}"         
    access_config {         
         nat_ip = "${var.EXT_IP_CREATE ? google_compute_address.external.address : 0 }"         
        }     
    }

If the resource google_compute_address.external has not been created, I need to set nat_ip to null or in other words 0.

That looks like it should work but it does not.

When setting EXT_IP_CREATE to true TF succeeds to create the resource. When setting it to false I receive the following error:

Error: Error running plan: 1 error(s) occurred:

* module.compute-dbma-dev.google_compute_instance.compute: 1 error(s) occurred:

* module.compute-dbma-dev.google_compute_instance.compute: Resource 'google_compute_address.external' not found for variable 'google_compute_address.external.address'

When I explicitly pass nat_ip = 0 TF recognizes the blank value and successfully creates the compute instances without the external IP.

Im currently on Terraform version Terraform v0.11. There is probably a super simple solution but I am just starting out with conditionals in TF and I getting stuck here.

Thanks in advance!

So your intention to do an optional argument with null is not possible before 0.12, but your real problem here is you need to set it for all of the network_interface. — Matthew Schuchard
– Matthew Schuchard, Commented Mar 13, 2019 at 17:57

a stone arachnid · Accepted Answer · 2019-05-19 16:03:54Z

1

Two ways to fix that:

TF_WARN_OUTPUT_ERRORS=1 terraform apply
${element(concat(google_compute_address.*.address, list("")), 0)}

edited May 19, 2019 at 16:03

a stone arachnid

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answered Mar 13, 2019 at 19:30

victor m

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2 Comments

glux Over a year ago

Neither 1 or 2 worked. For 1, I am still receiving the same resource not found for variable error. For 2, I am receiving this: Error: resource 'google_compute_instance.compute' config: unknown resource 'google_compute_address.*' referenced in variable google_compute_address.*.address

victor m Over a year ago

try: ${element(concat(google_compute_address.external.*.address, list("")), 0)}"

Jimmy Huang · Accepted Answer · 2019-05-19 03:28:07Z

When I tried to use a similar conditional, I get the following error:

* google_compute_instance.main: __builtin_StringToInt: strconv.ParseInt: parsing "": invalid syntax in:

${var.external_ip != "" ? var.external_ip : 0}

I do not see how the external IP can be conditionally attached, based on how GCP API works currently [1]:

networkInterfaces[].accessConfigs[].natIP => string

An external IP address associated with this instance. Specify an unused static external IP address available to the project or leave this field undefined to use an IP from a shared ephemeral IP address pool. If you specify a static external IP address, it must live in the same region as the zone of the instance.

[1] https://cloud.google.com/compute/docs/reference/rest/v1/instances

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