config: Add joinf function?

[radeksimko]

I caught myself writing the following code I don't like at all:

resource "aws_instance" "worker" {
  ami = "${lookup(var.aws_coreos_ami, var.aws_region)}"
  instance_type = "m3.medium"
  availability_zone = "${var.aws_az_name}"

  user_data = <<USER_DATA
#cloud-config
coreos:
  flannel:
    etcd_endpoints: http://${aws_instance.etcd.0.private_ip}:4001,http://${aws_instance.etcd.1.private_ip}:4001,http://${aws_instance.etcd.2.private_ip}:4001
USER_DATA
}

See the list of etcd endpoints which is not scalable at all, just because I have to provide a list of IPs with protocol + port number.

So I was thinking this could be much easier and scalable with hypothetical function joinf (name coming from join + format):

resource "aws_instance" "worker" {
  ami = "${lookup(var.aws_coreos_ami, var.aws_region)}"
  instance_type = "m3.medium"
  availability_zone = "${var.aws_az_name}"

  user_data = <<USER_DATA
#cloud-config
coreos:
  flannel:
    etcd_endpoints: ${joinf(",", "http://%s:4001", aws_instance.etcd.*.private_ip)}
USER_DATA
}

Any ideas for better name / reservations? I may send a PR at some point, but it would be nice to have a few 👍 or 👎 (+ reasons ideally).

[radeksimko]

This can be now done using a new function formatlist:

${join(",", formatlist("http://%s:4001", aws_instance.etcd.*.private_ip))}

I'm gonna close this as the above approach feels a bit cleaner than having one function that does two things (join + formatlist).

Thanks @josharian for making it happen! 😺

[ghost]

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