packer-cn/website/source/intro/getting-started/parallel-builds.html.markdown

---
layout: "intro"
page_title: "Parallel Builds"
prev_url: "/intro/getting-started/provision.html"
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---

# Parallel Builds

So far we've shown how Packer can automatically build an image and provision it.
This on its own is already quite powerful. But Packer can do better than that.
Packer can create multiple images for multiple platforms _in parallel_, all
configured from a single template.

This is a very useful and important feature of Packer. As an example,
Packer is able to make an AMI and a VMware virtual machine
in parallel provisioned with the _same scripts_, resulting in near-identical
images. The AMI can be used for production, the VMware machine can be used
for development. Or, another example, if you're using Packer to build
[software appliances](http://en.wikipedia.org/wiki/Software_appliance),
then you can build the appliance for every supported platform all in
parallel, all configured from a single template.

Once you start taking advantage of this feature, the possibilities begin
to unfold in front of you.

Continuing on the example in this getting started guide, we'll build
a [DigitalOcean](http://www.digitalocean.com) image as well as an AMI. Both
will be near-identical: bare bones Ubuntu OS with Redis pre-installed.
However, since we're building for both platforms, you have the option of
whether you want to use the AMI, or the DigitalOcean snapshot. Or use both.

## Setting Up DigitalOcean

[DigitalOcean](https://www.digitalocean.com/) is a relatively new, but
very popular VPS provider that has popped up. They have a quality offering
of high performance, low cost VPS servers. We'll be building a DigitalOcean
snapshot for this example.

In order to do this, you'll need an account with DigitalOcean.
[Sign up for an account now](https://www.digitalocean.com/). It is free
to sign up. Because the "droplets" (servers) are charged hourly, you
_will_ be charged $0.01 for every image you create with Packer. If
you're not okay with this, just follow along.

<div class="alert alert-block alert-warn">
<strong>Note!</strong> I want to repeat, in case you didn't see above:
You <em>will</em> be charged $0.01 by DigitalOcean per image created with Packer
because of the time the "droplet" is running.
</div>

Once you sign up for an account, grab your client ID and API key from
the [DigitalOcean API access page](https://www.digitalocean.com/api_access).
Save these values somewhere, you'll need them in a second.

## Modifying the Template

We now have to modify the template to add DigitalOcean to it. Modify the
template we've been using and add the following JSON object to the `builders`
array.

<pre class="prettyprint">
{
  "type": "digitalocean",
  "api_key": "INSERT API KEY HERE",
  "client_id": "INSERT CILENT ID HERE"
}
</pre>

Fill in your `api_key` and `client_id` for DigitalOcean as necessary.
The entire template should now [look like this](https://gist.github.com/mitchellh/51a447e38e7e496eb29c).

Additional builders are simply added to the `builders` array in the template.
This tells Packer to build multiple images. The builder `type` values don't
even need tdo be different! In fact, if you wanted to build multiple AMIs,
you can do that as well.

Validate the template with `packer validate`. This is always a good practice.

## Build

Now run `packer build example.json`. The output is too verbose to include
all of it, but a portion of it is reproduced below. Note that the ordering
and wording of the lines may be slightly different, but the effect is the
same.

```
$ packer build example.json
==> amazon-ebs: amazon-ebs output will be in this color.
==> digitalocean: digitalocean output will be in this color.

==> digitalocean: Creating temporary ssh key for droplet...
==> amazon-ebs: Creating temporary keypair for this instance...
==> amazon-ebs: Creating temporary security group for this instance...
==> digitalocean: Creating droplet...
==> amazon-ebs: Authorizing SSH access on the temporary security group...
==> amazon-ebs: Launching a source AWS instance...
==> digitalocean: Waiting for droplet to become active...
==> amazon-ebs: Waiting for instance to become ready...
==> digitalocean: Connecting to the droplet via SSH...
==> amazon-ebs: Connecting to the instance via SSH...
...
==> Builds finished. The artifacts of successful builds are:
--> amazon-ebs: AMIs were created:

us-east-1: ami-376d1d5e
--> digitalocean: A snapshot was created: packer-1371870364
```

As you can see, Packer builds both the Amazon and DigitalOcean images
in parallel. It outputs information about each in different colors
(although you can't see that in the block above) so that it is easy to identify.

At the end of the build, Packer outputs both of the artifacts created
(an AMI and a DigitalOcean snapshot). Both images created are bare bones
Ubuntu installations with Redis pre-installed.