182 lines
6.7 KiB
Markdown
182 lines
6.7 KiB
Markdown
---
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layout: "docs"
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page_title: "Terraform Settings - Configuration Language"
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sidebar_current: "docs-config-terraform"
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description: |-
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The "terraform" configuration section is used to configure some behaviors
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of Terraform itself.
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---
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# Terraform Settings
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-> **Note:** This page is about Terraform 0.12 and later. For Terraform 0.11 and
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earlier, see
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[0.11 Configuration Language: Terraform Settings](../configuration-0-11/terraform.html).
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The special `terraform` configuration block type is used to configure some
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behaviors of Terraform itself, such as requiring a minimum Terraform version to
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apply your configuration.
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## Terraform Block Syntax
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Terraform-specific settings are gathered together into `terraform` blocks:
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```hcl
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terraform {
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# ...
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}
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```
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Each `terraform` block can contain a number of settings related to Terraform's
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behavior. Within a `terraform` block, only constant values can be used;
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arguments may not refer to named objects such as resources, input variables,
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etc, and may not use any of the Terraform language built-in functions.
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The various options supported within a `terraform` block are described in the
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following sections.
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## Configuring a Terraform Backend
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The selected _backend_ for a Terraform configuration defines exactly where
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and how operations are performed, where [state](/docs/state/index.html) is
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stored, etc. Most non-trivial Terraform configurations will have a backend
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configuration that configures a remote backend to allow collaboration within
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a team.
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A backend configuration is given in a nested `backend` block within a
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`terraform` block:
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```hcl
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terraform {
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backend "s3" {
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# (backend-specific settings...)
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}
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}
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```
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More information on backend configuration can be found in
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[the _Backends_ section](/docs/backends/index.html).
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## Specifying a Required Terraform Version
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The `required_version` setting can be used to constrain which versions of
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the Terraform CLI can be used with your configuration. If the running version of
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Terraform doesn't match the constraints specified, Terraform will produce
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an error and exit without taking any further actions.
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When you use [child modules](./modules.html), each module
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can specify its own version requirements. The requirements of all modules
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in the tree must be satisfied.
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Use Terraform version constraints in a collaborative environment to
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ensure that everyone is using a specific Terraform version, or using at least
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a minimum Terraform version that has behavior expected by the configuration.
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The `required_version` setting applies only to the version of Terraform CLI.
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Various behaviors of Terraform are actually implemented by Terraform Providers,
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which are released on a cycle independent of Terraform CLI and of each other.
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Use [provider version constraints](./providers.html#provider-versions)
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to make similar constraints on which provider versions may be used.
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The value for `required_version` is a string containing a comma-separated
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list of constraints. Each constraint is an operator followed by a version
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number, such as `> 0.12.0`. The following constraint operators are allowed:
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* `=` (or no operator): exact version equality
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* `!=`: version not equal
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* `>`, `>=`, `<`, `<=`: version comparison, where "greater than" is a larger
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version number
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* `~>`: pessimistic constraint operator, constraining both the oldest and
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newest version allowed. For example, `~> 0.9` is equivalent to
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`>= 0.9, < 1.0`, and `~> 0.8.4`, is equivalent to `>= 0.8.4, < 0.9`
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Re-usable modules should constrain only the minimum allowed version, such
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as `>= 0.12.0`. This specifies the earliest version that the module is
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compatible with while leaving the user of the module flexibility to upgrade
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to newer versions of Terraform without altering the module.
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## Specifying Required Provider Versions
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The `required_providers` setting is a map specifying a version constraint for
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each provider required by your configuration.
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```hcl
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terraform {
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required_providers {
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aws = ">= 2.7.0"
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}
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}
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```
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Version constraint strings within the `required_providers` block use the
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same version constraint syntax as for
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[the `required_version` argument](#specifying-a-required-terraform-version)
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described above.
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When a configuration contains multiple version constraints for a single
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provider -- for example, if you're using multiple modules and each one has
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its own constraint -- _all_ of the constraints must hold to select a single
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provider version for the whole configuration.
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Re-usable modules should constrain only the minimum allowed version, such
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as `>= 1.0.0`. This specifies the earliest version that the module is
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compatible with while leaving the user of the module flexibility to upgrade
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to newer versions of the provider without altering the module.
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Root modules should use a `~>` constraint to set both a lower and upper bound
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on versions for each provider they depend on, as described in
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[Provider Versions](providers.html#provider-versions).
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An alternate syntax is also supported, but not intended for use at this time.
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It exists to support future enhancements.
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```hcl
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terraform {
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required_providers {
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aws = {
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version = ">= 2.7.0"
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}
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}
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}
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```
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## Experimental Language Features
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From time to time the Terraform team will introduce new language features
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initially via an opt-in experiment, so that the community can try the new
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feature and give feedback on it prior to it becoming a backward-compatibility
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constraint.
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In releases where experimental features are available, you can enable them on
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a per-module basis by setting the `experiments` argument inside a `terraform`
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block:
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```hcl
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terraform {
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experiments = [example]
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}
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```
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The above would opt in to an experiment named `example`, assuming such an
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experiment were available in the current Terraform version.
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Experiments are subject to arbitrary changes in later releases and, depending on
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the outcome of the experiment, may change drastically before final release or
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may not be released in stable form at all. Such breaking changes may appear
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even in minor and patch releases. We do not recommend using experimental
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features in Terraform modules intended for production use.
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In order to make that explicit and to avoid module callers inadvertently
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depending on an experimental feature, any module with experiments enabled will
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generate a warning on every `terraform plan` or `terraform apply`. If you
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want to try experimental features in a shared module, we recommend enabling the
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experiment only in alpha or beta releases of the module.
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The introduction and completion of experiments is reported in
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[Terraform's changelog](https://github.com/hashicorp/terraform/blob/master/CHANGELOG.md),
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so you can watch the release notes there to discover which experiment keywords,
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if any, are available in a particular Terraform release.
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