terraform: create list based on resource count

问题

We have a bunch of instances (I know... cattle, not pets, but in this case, these are really pets)

resource "aws_instance" "read_00" {
  count = "${var.read_00_count}"

resource "aws_instance" "read_01" {
  count = "${var.read_01_count}"

And we have an ELB where we want to dynamically add the instances based on their count variable, like so:

resource "aws_elb" "read_slaves" {
  instances = ["${aws_instance.read_.*.id}"]

But that doesn't work, of course.

Is it possible to dynamically create a list of instance ids ONLY if their count is not zero?

I know this goes against the grain, but if this is possible, that would be awesome.

回答1:

With Terraform 0.12 that will be much easier, but for now something like this would do:

[...]
resource "aws_instance" "read_01" {
  [...]
  count = "${var.read_01_count}"
  tags {
    Role = "read_slave"
  }
}

data "aws_instances" "read-slaves" {
  instance_tags {
    Role = "read_slave"
  }
  // optional filters
}

resource "aws_elb" "read_slaves" {
  instances = ["${data.aws_instances.read-slaves.ids}"]

  listener {
    ...
  }
}

Thus:

• tagging each instance which acts as a read slave
• collect the list of aws_intances
• create the aws_elb based on the collected data

来源：https://stackoverflow.com/questions/53280855/terraform-create-list-based-on-resource-count