Terraform conditionals - if variable does not exist

Question

I have the following condition:

resource "aws_elastic_beanstalk_application" "service" {
  appversion_lifecycle {
    service_role          = "service-role"
    delete_source_from_s3 = "${var.env == "production" ?   false : true}"
  }
}

If var.env is set to production, I get the result I want.

However if var.env is not defined, terraform plan will fail because the variable was never defined.
How can I get this to work, without ever having to define that variable?

Answer 1

Seems these days you can also use try to check if something is set.

try(var.env, false)

After that your code will work since var.env is now defined with the value false even if var.env was never defined somewhere.

https://www.terraform.io/docs/configuration/functions/try.html

Answer 2

if you are using Terraform 0.12 or later, you can assign the special value null to an argument to mark it as "unset".

variable "env" {
    type = "string"
    default = null
}

You can't just leave it blank, not with the current versions.