DEPRECATED: As of Terraform v0.12.0-alpha1 you should be able to use conditionals with list types.

Terraform Provider Conditional

Terraform currently lacks the ability to act on a ternary condition with anything but string values. This provider aims to be a stop-gap, providing conditionals for more complex types, until Terraform either gains broader conditional support, or support for custom functions (with HCL2).

Requirements

• Terraform 0.11.x
• Go 1.9+ and dep (for building)

Build the Provider

mkdir -p "${GOPATH:-${HOME}/go}/src/github.com/pdf"
cd "${GOPATH:-${HOME}/go}/src/github.com/pdf"
git clone https://github.com/pdf/terraform-provider-conditional.git && cd terraform-provider-conditional
dep ensure
go install

Using the Provider

If you're building the provider, follow the instructions to install it as a plugin. After placing it in your plugins directory, run terraform init to initialize it.

See the example directory for example declarations, below is a typical use-case:

/*
 * Declare the conditional.
 *
 * Typically the `if` field (and possibly `then`/`else` fields) will be
 * populated from variables within your module. When the value of `if` is
 * `true`, the value from `then` will populate the `result` field, otherwise
 * `result` will contain the value of the (optional) `else` field.
 *
 */
resource "conditional_list_of_string" "typical" {
  if   = "${true == true}"
  then = ["hello", "universe"]
  else = ["hello", "alternative universe"]
}

resource "some_resource" "instance" {
	list_field = ["${conditional_list_of_string.typical.result}"]
}

The currently available conditional resources are:

Resource name	Description	Example then/else/result values
conditional_list_of_string	A list of strings	["list", "of", "string"]
conditional_list_of_list_of_string	A list of lists of strings	[["a", "list"], ["another", "list"]]
conditional_list_of_map	A list of maps	[{a = "map"}, {another = "map"}]
conditional_map	A map	{a = "map"}

Due to the type system, condtionals supporting new data types for the then/else/result fields must be added explicitly. This is easy to do though, so if you require additional types for results, please feel free to open an issue.