AWS Network Interface Output IP not match

[garyjuano]

I noticed weird output behavior using aws_network_interface output

Here's my sample code below

resource "aws_network_interface" "testinterface" {
subnet_id ="subnet-xxxx"
private_ips_count = 2
tags = {
Name = "testing-only"
}
}

output "private_ips" {
value = "${aws_network_interface.testinterface.private_ips}"
}

Actual Output:
private_ips = [
"10.0.1.1",
"10.0.1.2",
"10.0.1.3",
]
Above output is correct

But when i changes the private_ips_count = 1 and run terraform apply command again. It still showing the previous output IP.

Actual Output:
private_ips = [
"10.0.1.1",
"10.0.1.2",
"10.0.1.3",
]

My expected should something like this(2 ips):
private_ips = [
"10.0.1.1",
"10.0.1.2",
]

Thanks,

[jpbuecken]

Same issue if you increase private_ips_count.

If you run terraform apply again the output is updated.

It looks like
aws_network_interface.testinterface.private_ip is not refreshed after private_ips_count has been changed.

And in terraform plan the following output may be useful, add (known after apply) to private_ips

      ~ private_ips       = [
            "10.18.82.30",
            "(known after apply)",
            (known after apply)
        ]
      ~ private_ips_count = 0 -> 2
        security_groups   = [
            "sg-08bcca43e47808c18",
        ]

Today with terraform 0.12.3 and aws provider 2.21:

       private_ips       = [
            "10.18.82.30",
        ]
      ~ private_ips_count = 0 -> 2
        security_groups   = [
            "sg-08bcca43e47808c18",
        ]

[cpalmer9]

Seeing same issue with Terraform v0.12.17 and provider.aws v2.41.0.
Basically, if you change the private_ips_count value on an existing aws_network_interface, it doesn't get refreshed for the apply and any variables that depend on that value are therefore incorrect. The ENI does get modified in AWS, it's just that Terraform doesn't seem to reflect that.
If you refresh after the apply, Terraform will be correct. Unfortunately for me, I needed the complete data for other resources during the apply.

[bflad]

To properly trigger the private_ips attribute to show as unknown (and therefore expected to have reference updates) when the private_ips_count argument is updated, a CustomizeDiff function can be added to the aws_network_interface resource using customdiff.ComputedIf(), e.g.

		CustomizeDiff: customdiff.Sequence(
			customdiff.ComputedIf("private_ips", func(_ context.Context, diff *schema.ResourceDiff, meta interface{}) bool {
				return diff.HasChange("private_ips_count")
			}),
		),

For acceptance testing this functionality, the TestAccAWSENI_PrivateIpsCount test steps can be updated to check the state private_ips.# value for updated amounts.

[rick-masters]

@bflad
Thanks for pointing out ComputedIf! I was really stuck without it but didn't know it until I stumbled upon your comment.

Most unfortunately, because the names private_ips and private_ips_count overlap, the SDK mistakenly deletes the pending change to private_ips_count. See hashicorp/terraform-plugin-sdk#715 just filed. That bug causes this example and pretty much only this example to fail (i.e private_ips_count has no effect). That's bad luck man.🤪

[github-actions]

This functionality has been released in v3.74.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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