website: document required_version

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

@@ -0,0 +1,77 @@
+---
+layout: "docs"
+page_title: "Configuring Terraform"
+sidebar_current: "docs-config-terraform"
+description: |-
+  Atlas is the ideal way to use Terraform in a team environment. Atlas will run Terraform for you, safely handle parallelization across different team members, save run history along with plans, and more.
+---
+
+# Terraform Configuration
+
+The `terraform` configuration section is used to configure Terraform itself,
+such as requiring a minimum Terraform version to execute a configuration.
+
+This page assumes you're familiar with the
+[configuration syntax](/docs/configuration/syntax.html)
+already.
+
+## Example
+
+Terraform configuration looks like the following:
+
+```
+terraform {
+    required_version = "> 0.7.0"
+}
+```
+
+## Description
+
+The `terraform` block configures the behavior of Terraform itself.
+
+The currently only allowed configuration within this block is
+`required_version`. This setting specifies a set of version constraints
+that must me bet to perform operations on this configuration. If the
+running Terraform version doesn't meet these constraints, an error
+is shown. See the section below dedicated to this option.
+
+**No value within the `terraform` block can use interpolations.** The
+`terraform` block is loaded very early in the execution of Terraform
+and interpolations are not yet available.
+
+## Specifying a Required Terraform Version
+
+The `required_version` setting can be used to require a specific version
+of Terraform. If the running version of Terraform doesn't match the
+constraints specified, Terraform will show an error and exit.
+
+When [modules](/docs/configuration/modules.html) are used, all Terraform
+version requirements specified by the complete module tree must be
+satisified. This means that the `required_version` setting can be used
+by a module to require that all consumers of a module also use a specific
+version.
+
+The value of this configuration is a comma-separated list of constraints.
+A constraint is an operator followed by a version, such as `> 0.7.0`.
+Constraints support the following operations:
+
+  * `=` (or no operator): exact version equality
+  * `!=`: version not equal
+  * `>`, `>=`, `<`, `<=`: version comparison, where "greater than" is
+    a larger version number.
+  * `~>`: pessimistic constraint operator. Example: for `~> 0.9`, this means
+    `>= 0.9, < 1.0`. Example: for `~> 0.8.4`, this means `>= 0.8.4, < 0.9`
+
+For modules, a minimum version is recommended, such as `> 0.8.0`. This
+minimum version ensures that a module operates as expected, but gives
+the consumer flexibility to use newer versions.
+
+## Syntax
+
+The full syntax is:
+
+```
+terraform {
+    required_version = VALUE
+}
+```

website/source/layouts/docs.erb

@@ -49,6 +49,10 @@
 					<a href="/docs/configuration/modules.html">Modules</a>
 					</li>
 
+					<li<%= sidebar_current("docs-config-terraform") %>>
+					<a href="/docs/configuration/terraform.html">Terraform</a>
+					</li>
+
 					<li<%= sidebar_current("docs-config-atlas") %>>
 					<a href="/docs/configuration/atlas.html">Atlas</a>
 					</li>