---
page_title: packer block reference
description: |-
  The `packer` block configures Packer behavior. Learn how to configure the `packer` in Packer templates written in HCL.  
---

# `packer` block

This topic provides reference information about the `packer` block. 

## Description

The `packer` block configures Packer version requirements and specifies which plugins to install upon initialization.

## 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 template, 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"
    }
  }
}
```

Using the `required_plugins` block to codify the plugins required for invoking a 
`packer build` on your template(s) is a great way to ensure consistent builds across
different platforms or hosts.

The block codifies two pieces of information that we've found critical to ensure reproducible builds:
1. **The source of a required plugin** indicates to users where a plugin where a plugin was downloaded from
and where to reach out if there are issues with the plugin. 
1. **The version of a required plugin** indicates to users the exact or minimum version needed for the build. 
This is a great way to pin approved versions of a plugin that can be installed across your environment or team.

For more information on plugins, refer to [Plugins](/packer/docs/plugins).

### Define plugin source
Specify the path to the plugin source code in the `source` field using the following format:

`<HOSTNAME>/[SUBFOLDER/]<NAMESPACE>/<TYPE>`

- `<Hostname>`: Specifies the hostname of the location or service that distributes the plugin. Packer only supports using `github.com` as the hostname when you install plugins using the `packer init` command. You can point to non-GitHub addresses, such as an internal proxy or plugin binary store, but Packer only pins the required version if you install the plugin using the `packer plugins install –path` command. Refer to the following documentation for additional information.
  - [`init` command](/packer/docs/commands/init)
  - [`plugins install`](/packer/docs/commands/plugins/install)
- `<Subfolder>`: The subfolder path segment is an optional part of the address that enables you to download plugin sources from custom addresses. You can specify a source containing up to 13 total path segments.   
- `<Namespace>`: An organizational namespace within the specified host. This often is the organization that publishes the plugin.
  Type: A short name for the platform or system the plugin manages. The type is usually the plugin's preferred local name.

For example, the value of the `source` field for a plugin named `myawesomecloud` is `github.com/hashicorp/myawesomecloud` if it belongs to the `hashicorp` namespace on the host `github.com`.

The actual repository that `myawesomecloud` comes from must always have the name format `github.com/hashicorp/packer-plugin-myawesomecloud`, but the `required_plugins` block omits the redundant `packer-plugin-` repository prefix for brevity.

## 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](/packer/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.
