how do i build a list of maps in terraform

Question

i would like to build a list of maps in terraform. Is there an operation that would let me do that.

eg: i would like to build the structure (from aws_instance.test.*.private_ip)

addresses = [
   {
     address = private_ip-1
   },
   {
     address = private_ip-2
   }
   ...
]

Answer 1

Apologies if this has already been resolved, I see that it's an older question.

I'm not sure if this is best practice, but this is the way I would attempt to reach the desired state.

Using the null_resource you'd be able to do the following:

variable "addresses" {
  type = "list"

  default = [
    "private_ip-1",
    "private_ip-2",
    "private_ip-3"
  ]
}

resource "null_resource" "test" {
  count = "${length(var.addresses)}"

  triggers {
    address = "${element(var.addresses, count.index)}"
  }
}

output "addresses" {
  value = "${null_resource.test.*.triggers}"
}

And have this output:

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

addresses = [
    {
        address = private_ip-1
    },
    {
        address = private_ip-2
    },
    {
        address = private_ip-3
    }
]

I'm currently on terraform 0.11.5, null_resource appears to have been added in 0.6.7

There are limitations to the null_resource triggers though. interpolated variables can only result in strings. So, unfortunately you won't be able to interpolate a value that would result in a list or a map; for example:

resource "null_resource" "test" {
  triggers {
    mylist = "${var.addresses}"
  }
}

will result in an error

Error: null_resource.test: triggers (address): '' expected type 'string', got unconvertible type '[]interface {}'