AWS network_interface detaches instances

[stack72]

I am creating a solution for NAT in AWS that when a new member of a NAT autoscale group is created, it will attach itself to the network interface.

the code effectively works as follows:

/usr/local/bin/aws ec2 attach-network-interface --network-interface-id $ENI_ID --instance-id $INSTANCE_ID --device-index 1 --region $ZONE

The network interface is terraform managed:

resource "aws_eip" "nat_ip" {
  vpc = true
  network_interface = "${aws_network_interface.nat_eni.id}"
}

resource "aws_network_interface" "nat_eni" {
  subnet_id = "${aws_subnet.primary-public.id}"
  security_groups = ["${aws_security_group.nat.id}"]
  source_dest_check = false

  tags {
    Name = "NAT ENI"
  }
}

On subsequent Terraform runs the attached instance is removed from the network interface and EIP as it was not part of the initial creation

~ aws_network_interface.nat_eni
    attachment.#:                       "1" => "0"
    attachment.2655983607.device_index: "1" => "0"
    attachment.2655983607.instance:     "i-30003f9d" => ""

~ aws_eip.nat_ip
    instance: "i-b3efd01e" => ""

This feels like a sledgehammer approach - is this intended?

[ghost]

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