Terraform - output ec2 instance ids to calling shell script - amazon-web-services

Question

I am using 'terraform apply' in a shell script to create multiple EC2 instances. I need to output the list of generated IPs to a script variable & use the list in another sub-script. I have defined output variables for the ips in a terraform config file - 'instance_ips'
output "instance_ips" {
value = [
"${aws_instance.gocd_master.private_ip}",
"${aws_instance.gocd_agent.*.private_ip}"
]
}
However, the terraform apply command is printing entire EC2 generation output apart from the output variables.
terraform init \
-backend-config="region=$AWS_DEFAULT_REGION" \
-backend-config="bucket=$TERRAFORM_STATE_BUCKET_NAME" \
-backend-config="role_arn=$PROVISIONING_ROLE" \
-reconfigure \
"$TERRAFORM_DIR"
OUTPUT = $( terraform apply <input variables e.g -
var="aws_region=$AWS_DEFAULT_REGION">
-auto-approve \
-input=false \
"$TERRAFORM_DIR"
)
terraform output instance_ips
So the 'OUTPUT' script variable content is
Terraform command: apply Initialising the backend... Successfully
configured the backend "s3"! Terraform will automatically use this
backend unless the backend configuration changes. Initialising provider
plugins... Terraform has been successfully initialised!
.
.
.
aws_route53_record.gocd_agent_dns_entry[2]: Creation complete after 52s
(ID:<zone ............................)
aws_route53_record.gocd_master_dns_entry: Creation complete after 52s
(ID:<zone ............................)
aws_route53_record.gocd_agent_dns_entry[1]: Creation complete after 53s
(ID:<zone ............................)
Apply complete! Resources: 9 added, 0 changed, 0 destroyed. Outputs:
instance_ips = [ 10.39.209.155, 10.39.208.44, 10.39.208.251,
10.39.209.227 ]
instead of just the EC2 ips.
Firing the 'terraform output instance_ips' is throwing a 'Initialisation Required' error which I understand means 'terraform init' is required.
Is there any way to suppress ec2 generation & just print output variables. if not, how to retrieve the IPs using 'terraform output' command w/o needing to do a terraform init ?

Answer 1

If I understood the context correctly, you can actually create a file in that directory & that file can be used by your sub-shell script. You can do it by using a null_resource OR "local_file".
Here is how we can use it in a modularized structure -
Using null_resource -
resource "null_resource" "instance_ips" {
triggers {
ip_file = "${sha1(file("${path.module}/instance_ips.txt"))}"
}
provisioner "local-exec" {
command = "echo ${module.ec2.instance_ips} >> instance_ips.txt"
}
}
Using local_file -
resource "local_file" "instance_ips" {
content = "${module.ec2.instance_ips}"
filename = "${path.module}/instance_ips.txt"
}