Conditionals in for_each loop around elastic IPs - terraform

Question

I have the following code and I would like to have a conditional that will only create an elastic IP if the instance is part of a public subnet (or based off of a boolean value if needed). This is the code that I currently have that works, but I want it to not create elastic IPs for resources on the private subnets:
locals {
instances_beta = {
my-ec2 = {
name = "myec2",
ami = "ami-029e27fb2fc8ce9d8",
instancetype = "t3.xlarge"
environment = "Beta",
securitygroups = [var.mysg],
subnetid = var.public-a,
elasticip = true
}
}
}
resource "aws_instance" "beta-instance" {
for_each = local.instances_beta
ami = each.value.ami
instance_type = each.value.instancetype
subnet_id = each.value.subnetid
key_name = "mykey"
vpc_security_group_ids = each.value.securitygroups
tags = {
Name = each.value.name
Environment = each.value.environment
}
}
resource "aws_eip" "beta-eip" {
for_each = local.instances_beta
instance = aws_instance.beta-instance[each.key].id
vpc = true
}
It sounds like count is the best way to do something like that, but I cannot do that as I am already using a for_each to achieve the resource creation. I was trying to do this with a nested for loop, but I cannot quite figure out how to get the syntax correct or if this is the best way to do it. For reference , the best resource I found on it was here around for_each conditionals: https://blog.gruntwork.io/terraform-tips-tricks-loops-if-statements-and-gotchas-f739bbae55f9

Answer 1

You can use for loop to create filtered map, for example:
for_each = {
for key, value in local.instances_beta: key => value if value.subnetid == var.public-a
}
It will filter local.instances_beta and leave items where subnetid equals var.public-a. You can adjust condition according to your needs.
More details in terraform documentation.