Terraform templatefile条件语句生成ansible库存文件

Question

// Terraform v0.14.9

# var.tf
variable "launch_zk" {
  type        = string
  description = "Whether to launch zookeeper or not"
  default     = false
}

# main.tf
resource "aws_instance" "zk_ec2" {
  count                = var.launch_zk ? var.zk_instance_count : 0
...
} 
 
# output.tf 
output "zk_ips" {
  description = "IPs of ZK instances"
  value = {
    for vm in aws_instance.zk_ec2 :
    vm.tags.Name => vm.private_ip
  }
}

resource "local_file" "AnsibleInventoryFile" {
  content = templatefile("ansible_inventory.tpl",
    {
      zk-private-ip     = var.zk_instance_count < 10 ? slice(aws_instance.zk_ec2.*.private_ip, 0, 3) : slice(aws_instance.zk_ec2.*.private_ip, 0, 5),
      zk-private-dns    = var.zk_instance_count < 10 ? slice(aws_instance.zk_ec2.*.private_dns, 0, 3) : slice(aws_instance.zk_ec2.*.private_dns, 0, 5),
    }
  )
  filename = "ansible_inventory"
}

# ansible_inventory.tpl
[zk_servers]
%{ for index, dns in zk-private-dns ~}
${zk-private-ip[index]} server_name=${dns}
%{ endfor ~}

This is what I am using and now I want to conditionally generate output file including ansible inventory file. It should include IP and DNS of zookeeper only if I am passing boolean true parameter to my "launch_zk" variable otherwise it should not print anything. Here I am not able to perform conditional statement in my output file and ansible template tpl file. Can someone tell me how can I get it working?

Here I will have to use multiple conditional statement like this but I am getting error given below

resource "local_file" "AnsibleInventoryFile" {
      content = templatefile("ansible_inventory.tpl",
        {
          zk-private-ip     = var.launch_zk ? var.zk_instance_count < 10 ? slice(aws_instance.zk_ec2.*.private_ip, 0, 3) : slice(aws_instance.zk_ec2.*.private_ip, 0, 5) : "",
          zk-private-dns    = var.launch ? var.zk_instance_count < 10 ? slice(aws_instance.zk_ec2.*.private_dns, 0, 3) : slice(aws_instance.zk_ec2.*.private_dns, 0, 5) : "",
        }
      )
      filename = "ansible_inventory"
    }


# Error
Error: Inconsistent conditional result types

  on output.tf line 67, in resource "local_file" "AnsibleInventoryFile":
  67:       zk-private-dns = var.launch_zk ? aws_instance.zk_ec2.*.private_dns : "",
    |----------------
    | aws_instance.zk_ec2 is empty tuple
    | var.launch_zk is "false"

The true and false result expressions must have consistent types. The given
expressions are tuple and string, respectively.

Answer 1

As docs explain, your condition must have consistent types :

The two result values may be of any type, but they must both be of the same type so that Terraform can determine what type the whole conditional expression will return without knowing the condition value.

In your case you return a list, and string:

#                              ? list                              : string    
zk-private-dns = var.launch_zk ? aws_instance.zk_ec2.*.private_dns : ""

The easiest way to ensure consistent types is by having an empty list :

zk-private-dns = var.launch_zk ? aws_instance.zk_ec2.*.private_dns : []

This change may require further changes in your code to account for the empty list