Terraform: How to dynamically create resources with conditional logic

background

As we (probably) know, Terraform does not support if statements.
Fortunately, we can countachieve the same result by using a specific parameter named .

We can think of it this way: the count can be set to 1, that is, a copy of the resource is obtained.

However, setting the same count parameter to 0 will not create any resources.

So, as mentioned, you don't need if/else statements at all, terrform uses conditional expressions in the following format:

<CONDITION> ? <TRUE_VAL> <FALSE_VAL>

All Terraform does is CONDITIONcompute boolean logic in , based on which, if the value is true, it will return TRUE_VAL; otherwise, if the result is false, it will return FALSE_VAL .

the case

For example, we will be migrating our existing AWS infrastructure (previously based on Ansible & Boto3 deployments) in terrraform.

This example is about ELB creation, which contains a target group and a listener .
Taken from a migration project I'm currently working on, it will actually show what I just explained:

resource "aws_lb_target_group" "tg" {
  count = var.target_group_addition ? 1 : 0
  name                 = "tg-${var.name}"
  port                 = var.tg_port
  protocol             = var.tg_protocol
  vpc_id               = var.vpc_id
  deregistration_delay = var.tg_deregistration_delay
  health_check {
    interval            = var.tg_healthcheck_interval
    path                = var.tg_healthcheck_path
    port                = "traffic-port"
    protocol            = var.tg_protocol
    timeout             = 5
    healthy_threshold   = 2
    unhealthy_threshold = 2
    matcher             = var.tg_healthcheck_success_code
  }
}

As you can see, the resource is only created if the booleanvar.target_group_add assigned to is set to aws_lb_target_group .true(1)

in conclusion

countThis is a very simple way of handling if statements in Terraform, and shows how to use properties in Terraform to do dynamic resource configuration when needed .

REF：

https://medium.com/swlh/terraform-how-to-use-conditionals-for-dynamic-resources-creation-6a191e041857

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