Unable to access list of "list of computed values" before terraform has run.

[josh-padnick]

I believe this is a bug in #2157. Given:

resource "aws_network_interface" "zk_eni_pool" {
  count = 3
  subnet_id = "subnet-123"
  security_groups = ["sg-123"]
}

I try the following:

resource "template_file" "mesos-environment" {
    filename = "${path.module}/files/user-data/mesos-environment.template"
    vars {
        eni_ip = "${join(",", aws_network_interface.zk_eni_pool.*.private_ips)}"
    }
}

This works fine once I've already done an initial terraform apply. But if I attempt to terraform apply for the first time, I receive the error:

Resource 'aws_network_interface.zk_eni_pool' does not have attribute 'private_ips' for variable 'aws_network_interface.zk_eni_pool.*.private_ips'

Replacing aws_network_interface.zk_eni_pool.*.private_ips with the following both work fine:

• aws_network_interface.zk_eni_pool.0.private_ips, or
• aws_network_interface.zk_eni_pool.0.subnet_id

Therefore, I interpret the root problem is that Terraform has a bug where it cannot access a list of "list of computed values". Thanks for your input.

[bryanstephens]

+1, now that #2157 fixed our issue with grabbing lists of private ips from ENIs this issue has been a pain for us with initializing our cluster for the first time as well.

[koendc]

The referenced commit fixes the issue in my case. Really not sure what is the impact of this on other parts of terraform though...

[phinze]

Hi folks!

The core of this issue is that the splat operator only has defined behavior for collecting lists of resources that were created using the count meta-parameter. The fact that it sometimes works to collect set elements is an incidental side effect of it's current implementation.

We'd definitely like to get the splat operator to fully support structured attributes, but today it does not, which is why you're getting the weird behavior described here.

Just reviewed our splat operator documentation and it looks pretty thin - I will bolster that in a PR linked back here.

[mitchellh]

Agreed this is fixed in my tests!

[ghost]

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