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layout: "docs"
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# Templates: Builders

Within the template, the builders section contains an array of all the
builders that Packer should use to generate a machine images for the template.

Builders are responsible for creating machines and generating 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:

<pre class="prettyprint">
{
  "builders": [
    ... one or more builder definitions here ...
  ]
}
</pre>

## Builder Definition

A single builder definition maps to exactly one [build](/docs/basics/terminology.html#term-build).
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:

<pre class="prettyprint">
{
  "type": "amazon-ebs",
  "access_key": "...",
  "secret_key": "..."
}
</pre>

## 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.
