packer/website/content/docs/templates/legacy_json_templates/builders.mdx

---
description: >
  The `builders` block contains builders that create machines and generate images. Learn how to configure the `builders` block in JSON templates for Packer.
page_title: builders reference for JSON templates
---

# `builders` reference for JSON templates

This topic provides reference information about the `builders` block in JSON templates.

`@include 'from-1.5/legacy-json-warning.mdx'`

## Introduction

The `builders` block contains an array of all the builders
that Packer should use to generate machine images for the template.

Builders create machines and generate images from them
for various platforms. For example, there are separate builders for EC2,
VMware, VirtualBox, etc. Packer comes with many builders by default, and can
also be extended to add new builders.

This documentation page will cover how to configure a builder in a template.
The specific configuration options available for each builder, however, must be
referenced from the documentation for that specific builder.

Within a template, a section of builder definitions looks like this:

```json
{
  "builders": [
    // ... one or more builder definitions here
  ]
}
```

## Builder Definition

A single builder definition maps to exactly one
[build](/packer/docs/terminology#builds). A builder definition is a
JSON object that requires at least a `type` key. The `type` is the name of the
builder that will be used to create a machine image for the build.

In addition to the `type`, other keys configure the builder itself. For
example, the AWS builder requires an `access_key`, `secret_key`, and some other
settings. These are placed directly within the builder definition.

An example builder definition is shown below, in this case configuring the AWS
builder:

```json
{
  "type": "amazon-ebs",
  "access_key": "...",
  "secret_key": "..."
}
```

## Named Builds

Each build in Packer has a name. By default, the name is just the name of the
builder being used. In general, this is good enough. Names only serve as an
indicator in the output of what is happening. If you want, however, you can
specify a custom name using the `name` key within the builder definition.

This is particularly useful if you have multiple builds defined that use the
same underlying builder. In this case, you must specify a name for at least one
of them since the names must be unique.

## Communicators

Every build is associated with a single
[communicator](/packer/docs/templates/legacy_json_templates/communicator). Communicators are used to
establish a connection for provisioning a remote machine (such as an AWS
instance or local virtual machine).

All the examples for the various builders show some communicator (usually SSH),
but the communicators are highly customizable so we recommend reading the
[communicator documentation](/packer/docs/templates/legacy_json_templates/communicator).