terraform/website/docs/configuration/terraform.html.md

layout	page_title	sidebar_current	description
docs	Terraform Settings - Configuration Language	docs-config-terraform	The "terraform" configuration section is used to configure some behaviors of Terraform itself.

Terraform Settings

-> Note: This page is about Terraform 0.12 and later. For Terraform 0.11 and earlier, see 0.11 Configuration Language: Terraform Settings.

The special terraform configuration block type is used to configure some behaviors of Terraform itself, such as requiring a minimum Terraform version to apply your configuration.

Terraform Block Syntax

Terraform-specific settings are gathered together into terraform blocks:

terraform {
  # ...
}

Each terraform block can contain a number of settings related to Terraform's behavior. Within a terraform block, only constant values can be used; arguments may not refer to named objects such as resources, input variables, etc, and may not use any of the Terraform language built-in functions.

The various options supported within a terraform block are described in the following sections.

Configuring a Terraform Backend

The selected backend for a Terraform configuration defines exactly where and how operations are performed, where state is stored, etc. Most non-trivial Terraform configurations will have a backend configuration that configures a remote backend to allow collaboration within a team.

A backend configuration is given in a nested backend block within a terraform block:

terraform {
  backend "s3" {
    # (backend-specific settings...)
  }
}

More information on backend configuration can be found in the Backends section.

Specifying a Required Terraform Version

The required_version setting can be used to constrain which versions of the Terraform CLI can be used with your configuration. If the running version of Terraform doesn't match the constraints specified, Terraform will produce an error and exit without taking any further actions.

When you use child modules, each module can specify its own version requirements. The requirements of all modules in the tree must be satisfied.

Use Terraform version constraints in a collaborative environment to ensure that everyone is using a specific Terraform version, or using at least a minimum Terraform version that has behavior expected by the configuration.

The required_version setting applies only to the version of Terraform CLI. Various behaviors of Terraform are actually implemented by Terraform Providers, which are released on a cycle independent of Terraform CLI and of each other. Use provider version constraints to make similar constraints on which provider versions may be used.

The value for required_version is a string containing a comma-separated list of constraints. Each constraint is an operator followed by a version number, such as > 0.12.0. The following constraint operators are allowed:

• = (or no operator): exact version equality

• !=: version not equal

• >, >=, <, <=: version comparison, where "greater than" is a larger version number

• ~>: pessimistic constraint operator, constraining both the oldest and newest version allowed. For example, ~> 0.9 is equivalent to >= 0.9, < 1.0, and ~> 0.8.4, is equivalent to >= 0.8.4, < 0.9

Re-usable modules should constrain only the minimum allowed version, such as >= 0.12.0. This specifies the earliest version that the module is compatible with while leaving the user of the module flexibility to upgrade to newer versions of Terraform without altering the module.

Specifying Required Provider Versions

The required_providers setting is a map specifying a version constraint for each provider required by your configuration.

terraform {
  required_providers {
    aws = ">= 2.7.0"
  }
}

Version constraint strings within the required_providers block use the same version constraint syntax as for the required_version argument described above.

When a configuration contains multiple version constraints for a single provider -- for example, if you're using multiple modules and each one has its own constraint -- all of the constraints must hold to select a single provider version for the whole configuration.

Re-usable modules should constrain only the minimum allowed version, such as >= 1.0.0. This specifies the earliest version that the module is compatible with while leaving the user of the module flexibility to upgrade to newer versions of the provider without altering the module.

Root modules should use a ~> constraint to set both a lower and upper bound on versions for each provider they depend on, as described in Provider Versions.

Experimental Language Features

From time to time the Terraform team will introduce new language features initially via an opt-in experiment, so that the community can try the new feature and give feedback on it prior to it becoming a backward-compatibility constraint.

In releases where experimental features are available, you can enable them on a per-module basis by setting the experiments argument inside a terraform block:

terraform {
  experiments = [example]
}

The above would opt in to an experiment named example, assuming such an experiment were available in the current Terraform version.

Experiments are subject to arbitrary changes in later releases and, depending on the outcome of the experiment, may change drastically before final release or may not be released in stable form at all. Such breaking changes may appear even in minor and patch releases. We do not recommend using experimental features in Terraform modules intended for production use.

In order to make that explicit and to avoid module callers inadvertently depending on an experimental feature, any module with experiments enabled will generate a warning on every terraform plan or terraform apply. If you want to try experimental features in a shared module, we recommend enabling the experiment only in alpha or beta releases of the module.

The introduction and completion of experiments is reported in Terraform's changelog, so you can watch the release notes there to discover which experiment keywords, if any, are available in a particular Terraform release.