234 lines
9.3 KiB
Markdown
234 lines
9.3 KiB
Markdown
---
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sidebar_current: "plugins-providers"
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---
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# Plugin Development: Providers
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This page documents how to add support for new [providers](/v2/providers/index.html)
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to Vagrant, allowing Vagrant to run and manage machines powered by a
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system other than VirtualBox. Prior to reading this, you should be familiar
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with the [plugin development basics](/v2/plugins/development-basics.html).
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Prior to developing a provider you should also be familiar with how
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[providers work](/v2/providers/index.html) from
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a user standpoint.
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<div class="alert alert-warn">
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<p>
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<strong>Warning: Advanced Topic!</strong> Developing plugins is an
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advanced topic that only experienced Vagrant users who are reasonably
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comfortable with Ruby should approach.
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</p>
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</div>
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## Example Provider: AWS
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The best way to learn how to write a provider is to see how one is
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written in practice. To augment this documentation, please heavily
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study the [vagrant-aws](https://github.com/mitchellh/vagrant-aws) plugin,
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which implements an AWS provider. The plugin is a good example of how to
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structure, test, and implement your plugin.
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## Definition Component
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Within the context of a plugin definition, new providers are defined
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like so:
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```ruby
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provider "my_cloud" do
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require_relative "provider"
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Provider
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end
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```
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Providers are defined with the `provider` method, which takes a single
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argument specifying the name of the provider. This is the name that is
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used with `vagrant up` to specify the provider. So in the case above,
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our provider would be used by calling `vagrant up --provider=my_cloud`.
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The block argument then lazily loads and returns a class that
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implements the `Vagrant.plugin(2, :provider)` interface, which is covered
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next.
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## Provider Class
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The provider class should subclass and implement
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`Vagrant.plugin(2, :provider)` which is an upgrade-safe way to let Vagrant
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return the proper parent class.
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This class and the methods that need to be implemented are
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[very well documented](https://github.com/mitchellh/vagrant/blob/master/lib/vagrant/plugin/v2/provider.rb). The documentation done on the class in the comments should be
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enough to understand what needs to be done.
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Viewing the [AWS provider class](https://github.com/mitchellh/vagrant-aws/blob/master/lib/vagrant-aws/provider.rb) as well as the
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[overall structure of the plugin](https://github.com/mitchellh/vagrant-aws) is recommended as a strong getting started point.
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Instead of going in depth over each method that needs to be implemented,
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the documentation will cover high-level but important points to help you
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create your provider.
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## Box Format
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Each provider is responsible for having its own box format. This is
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actually an extremely simple step due to how generic boxes are. Before
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explaining you should get familiar with the general
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[box file format](/v2/boxes/format.html).
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The only requirement for your box format is that the `metadata.json`
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file have a `provider` key which matches the name of your provider you
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chose above.
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In addition to this, you may put any data in the metadata as well
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as any files in the archive. Since Vagrant core itself doesn't care,
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it is up to your provider to handle the data of the box. Vagrant core
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just handles unpacking and verifying the box is for the proper
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provider.
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As an example of a couple box formats that are actually in use:
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* The `virtualbox` box format is just a flat directory of the contents
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of a `VBoxManage export` command.
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* The `vmware_fusion` box format is just a flat directory of the
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contents of a `vmwarevm` folder, but only including the bare essential
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files for VMware to function.
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* The `aws` box format is just a Vagrantfile defaulting some configuration.
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You can see an [example aws box unpacked here](https://github.com/mitchellh/vagrant-aws/tree/master/example_box).
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Before anything with your provider is even written, you can verify
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your box format works by doing `vagrant box add` with it. When you do
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a `vagrant box list` you can see what boxes for what providers are installed.
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You do _not need_ the provider plugin installed to add a box for that
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provider.
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<a name="actions"></a>
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## Actions
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Probably the most important concept to understand when building a
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provider is the provider "action" interface. It is the secret sauce that
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makes providers do the magic they do.
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Actions are built on top of the concept of
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[middleware](https://github.com/mitchellh/middleware), which
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allow providers to execute multiple distinct steps, have error recovery
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mechanics, as well as before/after behaviors, and much more.
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Vagrant core requests specific actions from your provider through the
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`action` method on your provider class. The full list of actions requested
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is listed in the comments of that method on the superclass. If your
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provider doesn't implement a certain action, then Vagrant core will show
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a friendly error, so don't worry if you miss any, things won't explode
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or crash spectacularly.
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Take a look at how the VirtualBox provider
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[uses actions to build up complicated multi-step processes](https://github.com/mitchellh/vagrant/blob/master/plugins/providers/virtualbox/action.rb#L287). The AWS provider [uses a similar process](https://github.com/mitchellh/vagrant-aws/blob/master/lib/vagrant-aws/action.rb).
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## Built-in Middleware
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To assist with common tasks, Vagrant ships with a set of
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[built-in middleware](https://github.com/mitchellh/vagrant/tree/master/lib/vagrant/action/builtin). Each of the middleware is well commented on the behavior and options
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for each, and using these built-in middleware is critical to building
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a well-behaved provider.
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These built-in middleware can be thought of as a standard library for
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your actions on your provider. The core VirtualBox provider uses these
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built-in middleware heavily.
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## Persisting State
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In the process of creating and managing a machine, providers generally need
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to store some sort of state somewhere. Vagrant provides each machine with
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a directory to store this state.
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As a use-case example for this, the VirtualBox provider stores the UUID
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of the VirtualBox virtual machine created. This allows the provider to track
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whether the machine is created, running, suspended, etc.
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The VMware provider actually copies the entire virtual machine into this
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state directory, complete with virtual disk drives and everything.
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The directory is available from the `data_dir` attribute of the `Machine`
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instance given to initialize your provider. Within middleware actions, the
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machine is always available via the `:machine` key on the environment. The
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`data_dir` attribute is a Ruby [Pathname](http://www.ruby-doc.org/stdlib-1.9.3/libdoc/pathname/rdoc/Pathname.html) object.
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It is important for providers to carefully manage all the contents of
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this directory. Vagrant core itself does little to clean up this directory.
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Therefore, when a machine is destroyed, be sure to clean up all the state
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from this directory.
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## Configuration
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Vagrant supports [provider-specific configuration](/v2/providers/configuration.html),
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allowing for users to finely tune and control specific providers from
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Vagrantfiles. It is easy for your custom provider to expose custom configuration
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as well.
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Provider-specific configuration is a special case of a normal
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[configuration plugin](/v2/plugins/configuration.html). When defining the
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configuration component, name the configuration the same as the provider,
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and as a second parameter, specify `:provider`, like so:
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```
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config("my_cloud", :provider) do
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require_relative "config"
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Config
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end
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```
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As long as the name matches your provider, and the second `:provider`
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parameter is given, Vagrant will automatically expose this as provider-specific
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configuration for your provider. Users can now do the following in their
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Vagrantfiles:
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```
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config.vm.provider :my_cloud do |config|
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# Your specific configuration!
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end
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```
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The configuration class returned from the `config` component in the plugin
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is the same as any other [configuration plugin](/v2/plugins/configuration.html),
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so read that page for more information. Vagrant automatically handles
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configuration validation and such just like any other configuration piece.
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The provider-specific configuration is available on the machine object
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via the `provider_config` attribute. So within actions or your provider class,
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you can access the config via `machine.provider_config`.
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<div class="alert alert-info">
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<p>
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<strong>Best practice:</strong> Your provider should <em>not require</em>
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provider-specific configuration to function, if possible. Vagrant
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practices a strong <a href="http://en.wikipedia.org/wiki/Convention_over_configuration">convention over configuration</a>
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philosophy. When a user installs your provider, they should ideally
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be able to <code>vagrant up --provider=your_provider</code> and
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have it just work.
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</p>
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</div>
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## Parallelization
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Vagrant supports parallelizing some actions, such as `vagrant up`, if the
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provider explicitly supports it. By default, Vagrant will not parallelize a
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provider.
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When parallelization is enabled, multiple [actions](#actions) may be run
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in parallel. Therefore, providers must be certain that their action stacks
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are thread-safe. The core of Vagrant itself (such as box collections, SSH,
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etc.) is thread-safe.
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Providers can explicitly enable parallelization by setting the `parallel`
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option on the provider component:
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```ruby
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provider("my_cloud", parallel: true) do
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require_relative "provider"
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Provider
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end
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```
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That is the only change that is needed to enable parallelization.
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