Allow upgrades only from supported versions

Introduces the `can_upgrade_from` field which is a list of supported
versions. We can control upgrade process now by this field, so user
won't start upgrade from the Fuel versions that we have not tested for
upgrade.

Change-Id: Id56a09845ade075fa4751c7eb164e065d5cad2ef
Closes-Bug: #1392756

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/before_upgrade_checker.py

@@ -242,3 +242,25 @@ class CheckUpgradeVersions(BaseBeforeUpgradeChecker):
 
         if err_msg:
             raise errors.WrongVersionError(err_msg)
+
+
+class CheckRequiredVersion(BaseBeforeUpgradeChecker):
+    """Checks that user's going to upgrade Fuel from the required version.
+
+    :param context: a context object with config and required space info
+    """
+
+    def __init__(self, context):
+        #: version of fuel which user wants to upgrade from
+        self.from_version = context.config.from_version
+        #: a list of versions from which user can upgrade
+        self.can_upgrade_from = context.config.can_upgrade_from
+
+    def check(self):
+        logger.info('Check required Fuel version')
+
+        if self.from_version not in self.can_upgrade_from:
+            raise errors.WrongVersionError(
+                'Cannot upgrade from Fuel {0}. You can upgrade only from '
+                'one of next versions: {1}'.format(
+                    self.from_version, ', '.join(self.can_upgrade_from)))

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/checker_manager.py

@@ -26,6 +26,7 @@ from fuel_upgrade.engines.openstack import OpenStackUpgrader
 from fuel_upgrade.before_upgrade_checker import CheckFreeSpace
 from fuel_upgrade.before_upgrade_checker import CheckNoRunningOstf
 from fuel_upgrade.before_upgrade_checker import CheckNoRunningTasks
+from fuel_upgrade.before_upgrade_checker import CheckRequiredVersion
 from fuel_upgrade.before_upgrade_checker import CheckUpgradeVersions
 
 
@@ -51,6 +52,7 @@ class CheckerManager(object):
     CHECKERS_MAPPING = {
         DockerUpgrader: [
             CheckUpgradeVersions,
+            CheckRequiredVersion,
             CheckFreeSpace,
             CheckNoRunningTasks,
             CheckNoRunningOstf],

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/config.py

@@ -228,6 +228,8 @@ def config(update_path, admin_password):
     """
     fuel_config_path = '/etc/fuel/'
 
+    can_upgrade_from = ['5.1.1']
+
     current_fuel_version_path = '/etc/fuel/version.yaml'
     new_upgrade_version_path = join(update_path, 'config/version.yaml')
 

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/engines/openstack.py

@@ -260,16 +260,17 @@ class OpenStackUpgrader(UpgradeEngine):
         metadata_path = self.config.openstack['metadata']
 
         # do nothing in case of metadata.yaml absence - just assume
-        # that we full repos
+        # that we have full repos
         if not os.path.exists(metadata_path):
             return
 
         with io.open(metadata_path, 'r', encoding='utf-8') as f:
-            metadata = yaml.load(f)
+            metadata = yaml.load(f) or {}
 
         # keep diff-based releases
         releases = filter(
-            lambda r: r['version'] in metadata['diff_releases'], releases)
+            lambda r: r['version'] in metadata.get('diff_releases', {}),
+            releases)
 
         # inject repos from base releases
         for release in releases:

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/tests/test_before_upgrade_checker.py

@@ -17,10 +17,12 @@
 import mock
 
 import requests
+import six
 
 from fuel_upgrade.before_upgrade_checker import CheckFreeSpace
 from fuel_upgrade.before_upgrade_checker import CheckNoRunningOstf
 from fuel_upgrade.before_upgrade_checker import CheckNoRunningTasks
+from fuel_upgrade.before_upgrade_checker import CheckRequiredVersion
 from fuel_upgrade.before_upgrade_checker import CheckUpgradeVersions
 from fuel_upgrade import errors
 from fuel_upgrade.tests.base import BaseTestCase
@@ -202,3 +204,26 @@ class TestCheckUpgradeVersions(BaseTestCase):
             err_msg,
             self.checker.check)
         compare_mock.assert_called_once_with('0', '9999')
+
+
+class TestCheckRequiredVersions(BaseTestCase):
+
+    def get_checker(self, user_conf={}):
+        config = self.fake_config
+
+        for key, value in six.iteritems(user_conf):
+            setattr(config, key, value)
+
+        return CheckRequiredVersion(mock.Mock(config=config))
+
+    def test_check_support_version(self):
+        checker = self.get_checker({
+            'from_version': '5.1.1',
+            'can_upgrade_from': ['5.1.1']})
+        checker.check()
+
+    def test_check_unsupport_version(self):
+        checker = self.get_checker({
+            'from_version': '5.1',
+            'can_upgrade_from': ['5.1.1']})
+        self.assertRaises(errors.WrongVersionError, checker.check)