Upgrades, show appropriate error if nailgun isn't running

Show a message to user for what to do if nailgun isn't
running when user starts the upgrade.

Change-Id: Iaabd281c43369884192fc34c85a293b70a9052ac
Closes-bug: #1366848

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/before_upgrade_checker.py

@@ -17,6 +17,7 @@
 import abc
 import logging
 
+import requests
 import six
 
 from fuel_upgrade import errors
@@ -55,7 +56,13 @@ class CheckNoRunningTasks(BaseBeforeUpgradeChecker):
         running tasks
         """
         logger.info('Check nailgun tasks')
-        tasks = self.nailgun_client.get_tasks()
+
+        try:
+            tasks = self.nailgun_client.get_tasks()
+        except requests.ConnectionError:
+            raise errors.NailgunIsNotRunningError(
+                'Cannot connect to rest api service')
+
         logger.debug('Nailgun tasks {0}'.format(tasks))
 
         running_tasks = filter(

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/cli.py

@@ -64,6 +64,8 @@ def handle_exception(exc):
         print(messages.docker_is_dead)
     elif isinstance(exc, errors.UpgradeVerificationError):
         print(messages.health_checker_failed)
+    elif isinstance(exc, errors.NailgunIsNotRunningError):
+        print(messages.nailgun_is_not_running)
 
     sys.exit(-1)
 

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/errors.py

@@ -75,3 +75,7 @@ class WrongVersionError(FuelUpgradeException):
 
 class UnsupportedActionTypeError(FuelUpgradeException):
     pass
+
+
+class NailgunIsNotRunningError(FuelUpgradeException):
+    pass

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/messages.py

@@ -37,6 +37,15 @@ https://bugs.launchpad.net/fuel/+bug/1359725
 """
 
 
+nailgun_is_not_running = """
+REST API service (nailgun) is not running. Unable to verify that
+there are no running tasks.
+
+Use `--no-check` as a parameter for upgrade script to skip all
+pre-upgrade checks.
+"""
+
+
 health_checker_failed = """
 Couldn't start some of the services, try to run upgrade again.
 """

fuel_upgrade_system/fuel_upgrade/fuel_upgrade/tests/test_before_upgrade_checker.py

@@ -16,6 +16,8 @@
 
 import mock
 
+import requests
+
 from fuel_upgrade.before_upgrade_checker import CheckFreeSpace
 from fuel_upgrade.before_upgrade_checker import CheckNoRunningTasks
 from fuel_upgrade.before_upgrade_checker import CheckUpgradeVersions
@@ -56,6 +58,17 @@ class TestCheckNoRunningTasks(BaseTestCase):
         checker.check()
         self.called_once(get_tasks_mock)
 
+    @mock.patch('fuel_upgrade.before_upgrade_checker.NailgunClient.get_tasks',
+                side_effect=requests.ConnectionError(''))
+    def test_check_raises_error_if_nailgun_is_not_running(
+            self, get_tasks_mock):
+        checker = CheckNoRunningTasks(self.config)
+        self.assertRaisesRegexp(
+            errors.NailgunIsNotRunningError,
+            'Cannot connect to rest api service',
+            checker.check)
+        self.called_once(get_tasks_mock)
+
 
 @mock.patch('fuel_upgrade.before_upgrade_checker.utils.find_mount_point',
             side_effect=['/var', '/var', '/etc'])