Allow user to specify mutual exclusive variables

[pasalkarsachin1]

Current Terraform Version

Terraform v0.11.11
+ provider.aws v2.16.0
+ provider.local v1.2.2
+ provider.null v2.1.2

Use-cases

We have use case in AWS lambda where we either want our user to provide the artifactory path for lambda code or his own code. There are 2 variables used as download artifactory needs local-exec mechanism where are local file needs archive zip way.

Right now, user can provide both options. We want options in variable to mar another variable as mutually exclusive

Attempted Solutions

N/A

Proposal

variable "local_file_content" { description = "If you have file present on owned tf, Mutually exclusive with download_location" type = "string" default = "" exclusive= ["download_location"] }

References

NA

[apparentlymart]

Thanks for this feature request, and sorry for the long delay in responding to it.

#34955 has recently been merged for inclusion in the forthcoming Terraform v1.9 release, and will allow input variable validation rules to refer to other symbols (including other input variables) declared in the same module.

That means it'll now be possible to write a validation rule that checks to ensure that at least one of two variables is null:

variable "a" {
  type    = string
  default = null

  # Optional: if you also want to require that _at least one_ be set.
  validation {
    condition = (var.a != null || var.b != null)
    error_message = "Must set either 'a' or 'b'."
  }
}

variable "b" {
  type    = string
  default = null

  validation {
    condition = (var.a == null || var.b == null)
    error_message = "Cannot set both 'a' and 'b'."
  }
}

This does require making a seemingly-arbitrary decision about which of the two variables to hook the validation rule onto, which will then dictate which one Terraform indicates as being the problem in its error message. In this example I chose to report that at least one is required using a and that only one can be set using b, which is what I'd choose to do if I expected that a would be the more common choice than b, but of course this is a contrived example.

Thanks again!

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