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website/docs/language/expressions/version-constraints.html.md

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+---
+layout: "language"
+page_title: "Version Constraints - Configuration Language"
+---
+
+# Version Constraints
+
+Anywhere that Terraform lets you specify a range of acceptable versions for
+something, it expects a specially formatted string known as a version
+constraint. Version constraints are used when configuring:
+
+- [Modules](/docs/configuration/blocks/modules/index.html)
+- [Provider requirements](./provider-requirements.html)
+- [The `required_version` setting](./terraform.html#specifying-a-required-terraform-version) in the `terraform` block.
+
+## Version Constraint Syntax
+
+Terraform's syntax for version constraints is very similar to the syntax used by
+other dependency management systems like Bundler and NPM.
+
+```hcl
+version = ">= 1.2.0, < 2.0.0"
+```
+
+A version constraint is a [string literal](/docs/configuration/expressions/strings.html)
+containing one or more conditions, which are separated by commas.
+
+Each condition consists of an operator and a version number.
+
+Version numbers should be a series of numbers separated by periods (like
+`1.2.0`), optionally with a suffix to indicate a beta release.
+
+The following operators are valid:
+
+- `=` (or no operator): Allows only one exact version number. Cannot be combined
+  with other conditions.
+
+- `!=`: Excludes an exact version number.
+
+- `>`, `>=`, `<`, `<=`: Comparisons against a specified version, allowing
+  versions for which the comparison is true. "Greater-than" requests newer
+  versions, and "less-than" requests older versions.
+
+- `~>`: Allows only the _rightmost_ version component to increment. For example,
+  to allow new patch releases within a specific minor release, use the full
+  version number: `~> 1.0.4` will allow installation of `1.0.5` and `1.0.10`
+  but not `1.1.0`. This is usually called the pessimistic constraint operator.
+
+## Version Constraint Behavior
+
+A version number that meets every applicable constraint is considered acceptable.
+
+Terraform consults version constraints to determine whether it has acceptable
+versions of itself, any required provider plugins, and any required modules. For
+plugins and modules, it will use the newest installed version that meets the
+applicable constraints.
+
+If Terraform doesn't have an acceptable version of a required plugin or module,
+it will attempt to download the newest version that meets the applicable
+constraints.
+
+If Terraform isn't able to obtain acceptable versions of external dependencies,
+or if it doesn't have an acceptable version of itself, it won't proceed with any
+plans, applies, or state manipulation actions.
+
+Both the root module and any child module can constrain the acceptable versions
+of Terraform and any providers they use. Terraform considers these constraints
+equal, and will only proceed if all of them can be met.
+
+A prerelease version is a version number that contains a suffix introduced by
+a dash, like `1.2.0-beta`. A prerelease version can be selected only by an
+_exact_ version constraint (the `=` operator or no operator). Prerelease
+versions do not match inexact operators such as `>=`, `~>`, etc.
+
+## Best Practices
+
+### Module Versions
+
+- When depending on third-party modules, require specific versions to ensure
+  that updates only happen when convenient to you.
+
+- For modules maintained within your organization, specifying version ranges
+  may be appropriate if semantic versioning is used consistently or if there is
+  a well-defined release process that avoids unwanted updates.
+
+### Terraform Core and Provider Versions
+
+- Reusable modules should constrain only their minimum allowed versions of
+  Terraform and providers, such as `>= 0.12.0`. This helps avoid known
+  incompatibilities, while allowing the user of the module flexibility to
+  upgrade to newer versions of Terraform 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.