Fix Py27 cloud-config ordering

On Py27, the yaml module implementation uses a normal dictionary for
implementation, resulting in arbitrary order for the parsed yaml.

If the config option cloud_config_plugins is not set or empty, fallback
to the default order defined in the factory.

Config option `cloud_config_plugins` is now used for filtering the cloud
config plugins to be executed, which was the original intended behaviour.

Change-Id: I59ea56e473ab343a826ff8c38787cb7f11cebd27

cloudbaseinit/plugins/common/userdataplugins/cloudconfig.py

@@ -42,11 +42,14 @@ class CloudConfigPluginExecutor(object):
 
     def __init__(self, **plugins):
         def _lookup_priority(plugin):
+            all_plugins = (CONF.cloud_config_plugins or
+                           list(factory.PLUGINS.keys()))
+            # return the order from the config or default list
             try:
-                return CONF.cloud_config_plugins.index(plugin)
+                return all_plugins.index(plugin)
             except ValueError:
-                # If the plugin was not specified in the order
-                # list, then default to a sane and unreachable value.
+                # If plugin is not supported or does not exist
+                # default to a sane and unreachable value.
                 return DEFAULT_ORDER_VALUE
 
         self._expected_plugins = sorted(
@@ -67,10 +70,17 @@ class CloudConfigPluginExecutor(object):
         return cls(**content)
 
     def execute(self):
-        """Call each plugin, in the order requested by the user."""
+        """Call each plugin, in the order defined by _lookup_priority"""
         reboot = execcmd.NO_REBOOT
         plugins = factory.load_plugins()
         for plugin_name, value in self._expected_plugins:
+            if CONF.cloud_config_plugins:
+                try:
+                    CONF.cloud_config_plugins.index(plugin_name)
+                except ValueError:
+                    LOG.info("Plugin %r is disabled", plugin_name)
+                    continue
+
             method = plugins.get(plugin_name)
             if not method:
                 LOG.error("Plugin %r is currently not supported", plugin_name)

cloudbaseinit/tests/plugins/common/userdataplugins/test_cloudconfig.py

@@ -51,6 +51,23 @@ class CloudConfigPluginTests(unittest.TestCase):
         finally:
             CONF.cloud_config_plugins = orig
 
+    def test_default_priority(self):
+        expected = [
+            ('write_files', 0),
+            ('hostname', 3),
+            ('runcmd', 1),
+            ('invalid1', 1),
+            ('invalid2', 2),
+        ]
+
+        executor = cloudconfig.CloudConfigPluginExecutor(
+            runcmd=1,
+            invalid1=1,
+            hostname=3,
+            invalid2=2,
+            write_files=0)
+        self.assertEqual(expected, executor._expected_plugins)
+
     def test_executor_from_yaml(self):
         for invalid in (mock.sentinel.yaml, None, 1, int, '{}'):
             with self.assertRaises(cloudconfig.CloudConfigError):

doc/source/userdata.rst

@@ -247,8 +247,9 @@ The following cloud-config directives are supported:
           - ['echo', '1']
 
 
-The cloud-config directives are executed in the following order: write_files, set_timezone,
-set_hostname, ntp, runcmd.
+The cloud-config directives are executed by default in the following order: write_files,
+set_timezone, set_hostname, ntp, groups, users, runcmd. Use config option `cloud_config_plugins`
+to filter or to change the order of the cloud config plugins.
 
 The execution of set_hostname or runcmd can request a reboot if needed. The reboot
 is performed at the end of the cloud-config execution (after all the directives have been