Document how to implement a new deploy step

Change-Id: I1ea0f78ef3b8d1c2248352f88e5421ae0bdd5b7f

doc/source/admin/deploy-steps.rst

@@ -33,6 +33,11 @@ is a higher priority. If the same priority is used by deploy steps on different
 interfaces, the following resolution order is used: Power, Management, Deploy,
 BIOS, and RAID interfaces.
 
+Writing a Deploy Step
+---------------------
+
+Please refer to :doc:`/contributor/deploy-steps`.
+
 FAQ
 ===
 

doc/source/contributor/deploy-steps.rst

@@ -0,0 +1,62 @@
+Developing a new Deploy Step
+============================
+
+To support customized deployment step, implement a new method in an interface
+class and use the decorator ``deploy_step`` defined in
+``ironic/drivers/base.py``. For example, we will implement a ``do_nothing``
+deploy step in the ``AgentDeploy`` class.
+
+.. code-block:: python
+
+  class AgentDeploy(AgentDeployMixin, base.DeployInterface):
+      ...
+
+      @base.deploy_step(priority=200, argsinfo={
+          'test_arg': {
+              'description': (
+                  "This is a test argument."
+              ),
+              'required': True
+          }
+      })
+      def do_nothing(self, task, **kwargs):
+          return None
+
+After deployment of the baremetal node, check the updated deploy steps::
+
+    openstack baremetal node show $node_ident -f json -c driver_internal_info
+
+The above command outputs the ``driver_internal_info`` as following::
+
+  {
+    "driver_internal_info": {
+      ...
+      "deploy_steps": [
+        {
+          "priority": 200,
+          "interface": "deploy",
+          "step": "do_nothing",
+          "argsinfo":
+            {
+              "test_arg":
+                {
+                  "required": True,
+                  "description": "This is a test argument."
+                }
+            }
+        },
+        {
+          "priority": 100,
+          "interface": "deploy",
+          "step": "deploy",
+          "argsinfo": null
+        }
+      ],
+      "deploy_step_index": 1
+    }
+  }
+
+.. note::
+
+    Similarly, clean steps can be implemented using the ``clean_step``
+    decorator.

doc/source/contributor/index.rst

@@ -65,6 +65,7 @@ the developer community about any implementation using this functionality.
   Writing "vendor_passthru" methods <vendor-passthru>
   Creating new BIOS interfaces <bios_develop>
   Third party continuous integration testing <third-party-ci>
+  Writing Deploy or Clean Steps <deploy-steps>
 
 Testing Network Integration
 ---------------------------