Added empty metadata service: EmptyMetadataService

The empty metadata service can be used to run plugins that do not
rely on metadata service information, like setting NTP, MTU,
extending volumes, local scripts execution, licensing, etc.

It can be used also as a fallback metadata service, in case no other
previous metadata service could be loaded.

EmptyMetadataService does not support the following plugins:
  * cloudbaseinit.plugins.windows.createuser.CreateUserPlugin
  * cloudbaseinit.plugins.common.setuserpassword.SetUserPasswordPlugin
  * cloudbaseinit.plugins.common.sshpublickeys.SetUserSSHPublicKeysPlugin
  * cloudbaseinit.plugins.windows.winrmcertificateauth.ConfigWinRMCertificateAuthPlugin

If any of the plugins defined above are executed,
they will fail with exception NotExistingMetadataException. The reason
for the hardcoded failure is that these plugins rely on metadata to execute
correctly. If metadata like username or password is not provided,
these plugins can lock or misconfigure the user, leading to unwanted problems.

Implements: blueprint empty-metadata-provider
Change-Id: I5fb88a07bf72321d0f66b16d151bf6059b448580

cloudbaseinit/metadata/services/base.py

@@ -297,3 +297,32 @@ class BaseHTTPMetadataService(BaseMetadataService):
             raise
 
         return response
+
+
+class EmptyMetadataService(BaseMetadataService):
+
+    """Empty metadata service implementation.
+
+    The empty metadata service can be used to run plugins that do not
+    rely on metadata service information, like setting ntp, mtu, etc.
+    It can be used also as a fallback metadata service, in case no other
+    previous metadata service could be loaded.
+    """
+
+    def __init__(self):
+        super(EmptyMetadataService, self).__init__()
+
+    def _get_data(self, path):
+        pass
+
+    def load(self):
+        return True
+
+    def get_admin_username(self):
+        raise NotExistingMetadataException()
+
+    def get_admin_password(self):
+        raise NotExistingMetadataException()
+
+    def is_password_changed(self):
+        raise NotExistingMetadataException()

cloudbaseinit/tests/metadata/services/test_base.py

@@ -183,3 +183,27 @@ class TestBaseHTTPMetadataService(unittest.TestCase):
         ssl_error = requests.exceptions.SSLError()
         self._test_get_data(expected_response=ssl_error,
                             expected_value=exception.CertificateVerifyFailed)
+
+
+class TestEmptyMetadataService(unittest.TestCase):
+
+    def setUp(self):
+        self._service = base.EmptyMetadataService()
+
+    def test_get_name(self):
+        self.assertEqual(self._service.get_name(), 'EmptyMetadataService')
+
+    def test__get_data(self):
+        self.assertFalse(self._service._get_data('fake_path'))
+
+    def test_get_admin_username(self):
+        self.assertRaises(base.NotExistingMetadataException,
+                          self._service.get_admin_username)
+
+    def test_get_admin_password(self):
+        self.assertRaises(base.NotExistingMetadataException,
+                          self._service.get_admin_password)
+
+    def test_is_password_changed(self):
+        self.assertRaises(base.NotExistingMetadataException,
+                          self._service.is_password_changed)

doc/source/services.rst

@@ -338,3 +338,27 @@ Config options for `default` section:
 
     * retry_count (integer: 5)
     * retry_count_interval (integer: 4)
+
+EMPTY
+-----
+
+.. class:: cloudbaseinit.metadata.services.base.EmptyMetadataService
+
+The empty metadata service can be used to run plugins that do not
+rely on metadata service information, like setting NTP, MTU,
+extending volumes, local scripts execution, licensing, etc.
+
+It can be used also as a fallback metadata service, in case no other
+previous metadata service could be loaded.
+
+EmptyMetadataService does not support the following plugins:
+  * cloudbaseinit.plugins.windows.createuser.CreateUserPlugin
+  * cloudbaseinit.plugins.common.setuserpassword.SetUserPasswordPlugin
+  * cloudbaseinit.plugins.common.sshpublickeys.SetUserSSHPublicKeysPlugin
+  * cloudbaseinit.plugins.windows.winrmcertificateauth.ConfigWinRMCertificateAuthPlugin
+
+If any of the plugins defined above are executed,
+they will fail with exception NotExistingMetadataException. The reason
+for the hardcoded failure is that these plugins rely on metadata to execute
+correctly. If metadata like username or password is not provided,
+these plugins can lock or misconfigure the user, leading to unwanted problems.

tox.ini

@@ -1,9 +1,10 @@
 [tox]
 minversion = 1.6
-envlist = py27,py33,pep8
+envlist = docs,py37,pep8
 skipsdist = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} -U --force-reinstall {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
@@ -16,7 +17,7 @@ commands = python setup.py testr --testr-args='{posargs}'
 commands = flake8 {posargs}
 
 [testenv:cover]
-basepython = python2.7
+basepython = python3
 setenv =
   {[testenv]setenv}
   PYTHON=coverage run --source cloudbaseinit --parallel-mode