packer-cn/website/content/docs/templates/hcl_templates/blocks/packer.mdx

---
page_title: packer - Blocks
sidebar_title: <tt>packer</tt>
description: |-
  The "packer" configuration section is used to configure some behaviors
  of Packer itself.
---

# Packer Settings

`@include 'from-1.5/beta-hcl2-note.mdx'`

-> **Note:** The `packer` block is only available in Packer v1.6.5 and later.

The `packer` configuration block type is used to configure some
behaviors of Packer itself, such as the minimum required Packer version needed to
apply your configuration.

## Packer Block Syntax

Packer settings are gathered together into `packer` blocks:

```hcl
packer {
  # ...
}
```

Each `packer` block can contain a number of settings related to Packer's
behavior. Within a `packer` 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 Packer language built-in functions.

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

## Specifying a Required Packer Version

The `required_version` setting accepts a [version constraint
string,](#version-constraints) which specifies which versions of Packer
can be used with your configuration.

If the running version of Packer doesn't match the constraints specified,
Packer will produce an error and exit without taking any further actions.

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

## Specifying Plugin Requirements

-> **Note:** The `required_plugins` block is only available in Packer v1.7.0 and
later.

The `required_plugins` block specifies all of the plugins required by the
current config, mapping each local plugin name to a source address and a
version constraint.

```hcl
packer {
  required_plugins {
    happycloud = {
      version = ">= 2.7.0"
      source = "github.com/hashicorp/happycloud"
    }
  }
}
```

For more information, see [Plugins](/docs/plugins).

## Version Constraints

Anywhere that Packer lets you specify a range of acceptable versions for
something, it expects a specially formatted string known as a version
constraint.

### Version Constraint Syntax

Packer's syntax for version constraints is very similar to the syntax used by
other dependency management systems like Bundler and NPM.

```hcl
required_version = ">= 1.2.0, < 2.0.0"
```

A version constraint is a [string literal](/docs/templates/hcl_templates/expressions#string-literals)
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 the specified version, plus newer versions that only
  increase the _most specific_ segment of the specified version number. For
  example, `~> 0.9` is equivalent to `>= 0.9, < 1.0`, and `~> 0.8.4`, is
  equivalent to `>= 0.8.4, < 0.9`. This is usually called the pessimistic
  constraint operator.

### Version Constraint Behavior

A version number that meets every applicable constraint is considered acceptable.

Packer consults version constraints to determine whether it has acceptable
versions of itself.

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.