Attaching AWS security group to multiple EC2 instances - amazon-ec2

Question

I am spinning up multiple Amazon EC2 instances and need to attach a Security Group. I am able to achieve it for one EC2 instance but looking for solution for multiple EC2s. I am using TerraForm 0.12. Please let me know how can I use data resource :- data "aws_instances" (s).
Here is the code for single EC2 which i am trying to convert for multiple EC2s:
resource "aws_instance" "ec2_instance" {
count = "${var.ec2_instance_count}"
ami = "${data.aws_ami.app_qrm_ami.id}"
...
}
data "aws_instances" "ec2_instances" {
count = "${var.ec2_instance_count}"
filter {
name = "instance-id"
values = ["${aws_instance.ec2_instance.*.id[count.index]}"]
}
}
resource "aws_network_interface_sg_attachment" "sg_attachment" {
security_group_id = "${data.aws_security_group.security_group.id}"
network_interface_id = "${data.aws_instance.ec2_instance[count.index].network_interface_id}" //facing issues here.
}
I want to achieve this using data "aws_instances" #notice the (s). Thanks in advance.

Answer 1

For removing the Hard coding of ec2 AMI, you can use the following data provider:-
data "aws_ami" "amazon_linux" {
count = "${var.ec2_instance_count}"
most_recent = true
owners = ["amazon"]
filter {
name = "name"
values = [
"amzn-ami-hvm-*-x86_64-gp2",
]
}
filter {
name = "owner-alias"
values = [
"amazon",
]
}
}
For rendering the ami id:-
resource "aws_instance" "ec2_instance" {
count = "${var.ec2_instance_count}"
ami = "${data.aws_ami.amazon_linux[count.index].id}"
network_interface =
For getting network_interface_id:-
resource "aws_network_interface" "ec2_nic" {
count = "${var.ec2_instance_count}"
subnet_id = "${aws_subnet.public_a.id}"
private_ips = ["10.0.0.50"]
security_groups = ["${aws_security_group.web.id}"]
attachment {
instance = "${aws_instance.ec2_instance[count.index].id}"
}
}
resource "aws_network_interface_sg_attachment" "sg_attachment" {
security_group_id = "${data.aws_security_group.security_group.id}"
network_interface_id = "${aws_network_interface.ec2_ami[count.index].id}"
}

Answer 2

Thanks Karan, your answer solved the issue for me. Later the infra got fairly complex and I found a different and a smarter way to solve it. I would like to share with other people which might help TF community in future.
multiple internal SG {internal 0-7}and one external to all for creating different groups of swarm which allowed to communicate internal and selectively externally. Majorly used in Microsoft HPC grid.
resource "aws_instance" "ec2_instance" {
count = tonumber(var.mycount)
vpc_security_group_ids = [data.aws_security_group.external_security_group.id, element(data.aws_security_group.internal_security_group.*.id, count.index)]
...
}
resource "aws_security_group" "internal_security_group" {
count = tonumber(var.mycount)
name = "${var.internalSGname}${count.index}"
}
resource "aws_security_group" "external_security_group" {
name = ${var.external_sg_name}"
}