terraform - create instances on list of strings - terraform

Question

resource "aws_instance" "jenkins_worker_inst" {
for_each = toset(["peter", "nelson", "chris"])
provider = aws.region_worker
ami = data.aws_ssm_parameter.worker-linuxAmi.value
instance_type = var.instance-type
key_name = aws_key_pair.worker_key_pair.key_name
associate_public_ip_address = true
vpc_security_group_ids = [aws_security_group.jenkins_worker_sg.id]
subnet_id = aws_subnet.worker_subnet_1.id
tags = {
Name = each.key
}
depends_on = [aws_main_route_table_association.set-worker-default-rt-assoc, aws_instance.jenkins_master_inst]
provisioner "local-exec" {
command = <<EOF
#aws --debug --profile ${var.profile} ec2 wait instance-status-ok --region ${var.region_master} --instance-ids "${self.id}" ansible-playbook --verbose --extra-vars 'passed_in_hosts=tag_Name_${self.tags.Name}' ansible_templates/jenkins-worker-sample.yml
EOF
}
}
I am told that the for_each here should be able to make 3 instances, but it is making 1.
i have tried it with terraform 0.12 and 1.0.0. I really need a way to make the number of instances based on list of something

Answer 1

There are essentially 2 ways to accomplish what you are trying to do. One way is with the for_each meta-argument, which is what you attempted. The other way is by using count, which would look something this.
locals {
instance_names = ["peter", "nelson", "chris"]
}
resource "aws_instance" "jenkins_worker_inst" {
count = length(instance_names)
provider = aws.region_worker
ami = data.aws_ssm_parameter.worker-linuxAmi.value
instance_type = var.instance-type
key_name = aws_key_pair.worker_key_pair.key_name
associate_public_ip_address = true
vpc_security_group_ids = [aws_security_group.jenkins_worker_sg.id]
subnet_id = aws_subnet.worker_subnet_1.id
tags = {
Name = element(local.instance_names, count.index)
}
depends_on = [aws_main_route_table_association.set-worker-default-rt-assoc, aws_instance.jenkins_master_inst]
provisioner "local-exec" {
command = <<EOF
#aws --debug --profile ${var.profile} ec2 wait instance-status-ok --region ${var.region_master} --instance-ids "${self.id}" ansible-playbook --verbose --extra-vars 'passed_in_hosts=tag_Name_${self.tags.Name}' ansible_templates/jenkins-worker-sample.yml
EOF
}
}
The for_each meta-argument should work for Terraform v0.12.6+. If you tried using it in a version of Terraform prior to v0.12.6, then for_each would not yet be supported; you would only have count as an option.
You also stated that you tried it with Terraform v1.0+, which does support for_each. Without additional information (plan?), I can't tell you why that didn't work. However, I can say that sometimes Terraform does wonkey stuff and in the past, there have been breaking changes introduced in minor and patch versions, sometimes without announcement.
Finally, This Medium post does a pretty decent job of explaining the differences between count and for_each. But for your example, either should work just fine.