Terraform module sources and versions support variables and locals

Introduced 2026-04-29 · score 0.96

HOW TO USE IT

When selecting a module source or registry version from configuration values, use input variables marked `const = true`; you can reference them directly or through locals. Provide their values with a supported variable mechanism, then run `terraform init` after changing the module source or version.

variable "module_source" {
  type  = string
  const = true
}

module "example" {
  source = var.module_source
}

terraform plan -var='module_source=./<module-directory>'

variable "module_repo" {
  type  = string
  const = true
}

variable "module_ref" {
  type  = string
  const = true
}

locals {
  module_source = "git::https://example.com/${var.module_repo}.git?ref=${var.module_ref}"
}

module "example" {
  source = local.module_source
}

terraform plan -var='module_repo=<repository>' -var='module_ref=<branch-or-tag>'

variable "module_version" {
  type  = string
  const = true
}

module "example" {
  source  = "<registry-namespace>/<module>/<provider>"
  version = var.module_version
}

terraform plan -var='module_version=<version-constraint>'

WHY THIS HELPS

Select a module source or version using a configuration value.

REQUIREMENTS AND LIMITATIONS

Version: 1.15.0
const: Set to `true` for any input variable referenced by a module `source` or `version`; its value must be known during configuration loading.
source (required): Module source expression; it can reference constant input variables and local values.
version: Registry module version constraint; it can reference constant input variables and local values. Use only with a registry source.
-var 'NAME=VALUE': Set one root input variable value; the option can be repeated.
-var-file=FILENAME: Set root input variable values from a `.tfvars` file; the option can be repeated.
TF_VAR_name: Environment variable form for setting an input variable; replace `name` with the variable name.
Prerequisite: Terraform v1.15.0 introduced `const` variables for module source/version expressions.
Prerequisite: Run `terraform init` after modifying a module `source` or `version`.
Nested modules can use variables in module sources only when their input variables are declared `const = true`.
The release text states that variables and locals are supported in module source and version attributes, but the linked description examples only show `source`.

FIRST-PARTY EVIDENCE

Check the installed version and the source before using it. Entry JSON

Report a problem with this card

Tools change faster than your agent’s training data.

Changes

Terraform module sources and versions support variables and locals