Deprecate legacy heat driver

Log a warning about fedora-coreos Heat driver, with a note
encouraging users to migrate to modern CAPI drivers.

Change-Id: I45cf3bcf6e542319fed83613919d2e1398fcb2bb

doc/source/user/index.rst

@@ -13,6 +13,10 @@ best meets your needs and how to develop a driver for a new COE.
 Section 10-15 describe the low level OpenStack infrastructure that is
 created and managed by Magnum to support the COE's.
 
+.. warning::
+  The heat driver described here is deprecated in favor of the k8s_capi_helm
+  or k8s_cluster_api driver and will be removed in a future Magnum version.
+
 #. `Overview`_
 #. `Python Client`_
 #. `Horizon Interface`_

magnum/api/controllers/v1/cluster_template.py

@@ -269,6 +269,11 @@ class ClusterTemplatesController(base.Controller):
         "different storage driver, such as overlay2. overlay2 will be set "
         "as the default storage driver from Victoria cycle in Magnum.")
 
+    _heat_driver_deprecation_note = (
+        "The heat driver is deprecated in favor of the k8s_capi_helm or"
+        "k8s_cluster_api driver. Please migrate to one of the abovementioned."
+        "Heat driver will be removed in a future Magnum version.")
+
     def _generate_name_for_cluster_template(self, context):
         """Generate a random name like: zeta-22-model."""
 
@@ -432,6 +437,12 @@ class ClusterTemplatesController(base.Controller):
                           DeprecationWarning)
             LOG.warning(self._coreos_deprecation_note)
 
+        if (cluster_template_dict['coe'] == 'kubernetes' and
+                cluster_template_dict['cluster_distro'] == 'fedora-coreos'):
+            warnings.warn(self._heat_driver_deprecation_note,
+                          DeprecationWarning)
+            LOG.warning(self._heat_driver_deprecation_note)
+
         # NOTE(yuywz): We will generate a random human-readable name for
         # cluster_template if the name is not specified by user.
         arg_name = cluster_template_dict.get('name')

releasenotes/notes/deprecate-heat-driver-930d999afde1eece.yaml

@@ -0,0 +1,11 @@
+---
+deprecations:
+  - |
+    Deprecate the use of 'heat' driver in favor of modern
+    Kubernetes Cluster API based drivers: 'k8s_capi_helm' [1] or
+    'k8s_cluster_api' [2]. User still using 'heat' driver are encouraged to
+    migrate to one of the abovementioned as 'heat' driver will be removed in
+    the future.
+
+    [1] https://docs.openstack.org/magnum-capi-helm/latest/
+    [2] https://vexxhost.github.io/magnum-cluster-api/