Deploy interface that fully relies on custom deploy steps

This change adds a new deploy-interface custom-agent that is essentially
the direct deploy without the write_image step and without bootloader
handling. It's targeted at deployments that need to write the image
differently, while keeping all other aspects the same.

The existing AgentDeploy becomes a subclass of the new CustomAgentDeploy
class, serving as a convenient base class for downstream deploy
interfaces that use IPA.

Change-Id: Ie126ce677c79f102e382305650bddb7f09834483
Story: #2008719
Task: #42059

1 files changed, 24 insertions, 2 deletions

diff --git a/doc/source/contributor/deploy-steps.rst b/doc/source/contributor/deploy-steps.rst
index 21022b2b1..ae79e56f1 100644
--- a/doc/source/contributor/deploy-steps.rst
+++ b/doc/source/contributor/deploy-steps.rst
@@ -8,8 +8,9 @@ deploy step in the ``AgentDeploy`` class.
 
 .. code-block:: python
 
-  class AgentDeploy(AgentDeployMixin, base.DeployInterface):
-      ...
+  from ironic.drivers.modules import agent
+
+  class AgentDeploy(agent.AgentDeploy):
 
       @base.deploy_step(priority=200, argsinfo={
           'test_arg': {
@@ -22,6 +23,27 @@ deploy step in the ``AgentDeploy`` class.
       def do_nothing(self, task, **kwargs):
           return None
 
+If you want to completely replace the deployment procedure, but still have the
+agent up and running, inherit ``CustomAgentDeploy``:
+
+.. code-block:: python
+
+  from ironic.drivers.modules import agent
+
+  class AgentDeploy(agent.CustomAgentDeploy):
+
+      def validate(self, task):
+          super().validate(task)
+          # ... custom validation
+
+      @base.deploy_step(priority=80)
+      def my_write_image(self, task, **kwargs):
+          pass  # ... custom image writing
+
+      @base.deploy_step(priority=70)
+      def my_configure_bootloader(self, task, **kwargs):
+          pass  # ... custom bootloader configuration
+
 After deployment of the baremetal node, check the updated deploy steps::
 
     baremetal node show $node_ident -f json -c driver_internal_info