website: custom provisioner docs

website/source/docs/extend/provisioner.html.markdown

+---
+layout: "docs"
+---
+
+# Custom Provisioner Development
+
+Provisioners are the components of Packer that install and configure
+software into a running machine prior to turning that machine into an
+image. An example of a provisioner is the [shell provisioner](/docs/provisioners/shell.html),
+which runs shell scripts within the machines.
+
+Prior to reading this page, it is assumed you have read the page on
+[plugin development basics](/docs/extend/developing-plugins.html).
+
+Provisioner plugins implement the `packer.Provisioner` interface and
+are served using the `plugin.ServeProvisioner` function.
+
+<div class="alert alert-block">
+  <strong>Warning!</strong> This is an advanced topic. If you're new to Packer,
+  we recommend getting a bit more comfortable before you dive into writing
+  plugins.
+</div>
+
+
+## The Interface
+
+The interface that must be implemented for a provisioner is the
+`packer.Provisioner` interface. It is reproduced below for easy reference.
+The reference below also contains some basic documentation of what each of
+the methods are supposed to do.
+
+<pre class="prettyprint">
+// A provisioner is responsible for installing and configuring software
+// on a machine prior to building the actual image.
+type Provisioner interface {
+	// Prepare is called with a set of configurations to setup the
+	// internal state of the provisioner. The multiple configurations
+	// should be merged in some sane way.
+	Prepare(...interface{}) error
+
+	// Provision is called to actually provision the machine. A UI is
+	// given to communicate with the user, and a communicator is given that
+	// is guaranteed to be connected to some machine so that provisioning
+	// can be done.
+	Provision(Ui, Communicator)
+}
+</pre>
+
+### The "Prepare" Method
+
+The `Prepare` method for each provisioner is called prior to any runs with
+the configuration that was given in the template. This is passed in as
+an array of `interface{}` types, but is generally `map[string]interface{}`. The prepare
+method is responsible for translating this configuration into an internal
+structure, validating it, and returning any errors.
+
+For multiple parameters, they should be merged together into the final
+configuration, with later parameters overwriting any previous configuration.
+The exact semantics of the merge are left to the builder author.
+
+For decoding the `interface{}` into a meaningful structure, the
+[mapstructure](https://github.com/mitchellh/mapstructure) library is recommended.
+Mapstructure will take an `interface{}` and decode it into an arbitrarily
+complex struct. If there are any errors, it generates very human friendly
+errors that can be returned directly from the prepare method.
+
+While it is not actively enforced, **no side effects** should occur from
+running the `Prepare` method. Specifically, don't create files, don't launch
+virtual machines, etc. Prepare's purpose is solely to configure the builder
+and validate the configuration.
+
+The `Prepare` method is called very early in the build process so that
+errors may be displayed to the user before anything actually happens.
+
+### The "Provision" Method
+
+The `Provision` method is called when a machine is running and ready
+to be provisioned. The provisioner should do its real work here.
+
+The method takes two parameters: a `packer.Ui` and a `packer.Communicator`.
+The UI can be used to communicate with the user what is going on. The
+communicator is used to communicate with the running machine, and is
+guaranteed to be connected at this point.
+
+The provision method should not return until provisioning is complete.
+
+## Using the Communicator
+
+The `packer.Communicator` parameter and interface is used to communicate
+with running machine. The machine may be local (in a virtual machine or
+container of some sort) or it may be remote (in a cloud). The communicator
+interface abstracts this away so that communication is the same overall.
+
+The documentation around the [code itself](https://github.com/mitchellh/packer/blob/master/packer/communicator.go)
+is really great as an overview of how to use the interface. You should begin
+by reading this. Once you have read it, you can see some example usage below:
+
+<pre class="prettyprint">
+// Build the remote command.
+var cmd packer.RemoteCmd
+cmd.Command = "echo foo"
+
+// We care about stdout, so lets collect that into a buffer. Since
+// we don't set stderr, that will just be discarded.
+var stdout bytes.Buffer
+cmd.Stdout = &stdout
+
+// Start the command
+if err := comm.Start(&cmd); err != nil {
+  panic(err)
+}
+
+// Wait for it to complete
+cmd.Wait()
+
+// Read the stdout!
+fmt.Printf("Command output: %s", stdout.String())
+</pre>

website/source/layouts/docs.erb

@@ -63,7 +63,7 @@
 							<li><a href="/docs/extend/builder.html">Custom Builder</a></li>
 							<li><a href="/docs/extend/command.html">Custom Command</a></li>
 							<li><a href="/docs/extend/post-processor.html">Custom Post-Processor</a></li>
-							<li><a href="#">Custom Provisioner</a></li>
+							<li><a href="/docs/extend/provisioner.html">Custom Provisioner</a></li>
 						</ul>
 					</div><!--/.well -->
 				</div><!--/span-->