Allow service actions to be overridden

In order to allow child classes to use other means of controlling
service lifetime, this change introduces methods that call
systemd/upstart via charm-helpers by default but allow for something
else to be used in overrides.

The example use-case in question is the use of crm tools to restart
services:

crm_resource --restart --wait --node <node-name>

Which will restart a resource on a given node if it is running there or
return ENXIO otherwise.

Change-Id: Ifb16f6743296a1ef6dcb212cad517afd57270f7f
Closes-Bug: #1891160

charms_openstack/charm/classes.py

@@ -751,7 +751,7 @@ class HAOpenStackCharm(OpenStackAPICharm):
             ['a2query', '-s', 'openstack_https_frontend'])
         if check_enabled:
             subprocess.check_call(['a2ensite', 'openstack_https_frontend'])
-            ch_host.service_reload('apache2', restart_on_failure=True)
+            self.service_reload('apache2', restart_on_failure=True)
 
     def configure_apache(self):
         if self.apache_enabled():
@@ -928,7 +928,7 @@ class HAOpenStackCharm(OpenStackAPICharm):
                 subprocess.check_call(['a2enmod', module])
                 restart = True
         if restart:
-            ch_host.service_restart('apache2')
+            self.service_restart('apache2')
 
     def configure_tls(self, certificates_interface=None):
         """Configure TLS certificates and keys
@@ -969,7 +969,7 @@ class HAOpenStackCharm(OpenStackAPICharm):
                     os.path.join('/etc/apache2/ssl/', self.name))
                 if not os_utils.snap_install_requested() and changed:
                     self.configure_apache()
-                    ch_host.service_reload('apache2')
+                    self.service_reload('apache2')
 
                 self.remove_state('ssl.requested')
                 self.set_state('ssl.enabled', True)

charms_openstack/charm/core.py

@@ -685,6 +685,50 @@ class BaseOpenStackCharmActions(object):
         """
         return self.restart_map
 
+    def service_stop(self, service_name):
+        """Stop the specified service.
+
+        Meant to be overridden by child classes in scenarios where clustering
+        software like Pacemaker is used.
+
+        :param service_name: The service to stop.
+        :type service_name: str
+        """
+        ch_host.service_stop(service_name)
+
+    def service_start(self, service_name):
+        """Start the specified service.
+
+        Meant to be overridden by child classes in scenarios where clustering
+        software like Pacemaker is used.
+
+        :param service_name: The service to start.
+        :type service_name: str
+        """
+        ch_host.service_start(service_name)
+
+    def service_restart(self, service_name):
+        """Restart the specified service.
+
+        Meant to be overridden by child classes in scenarios where clustering
+        software like Pacemaker is used.
+
+        :param service_name: The service to restart.
+        :type service_name: str
+        """
+        ch_host.service_restart(service_name)
+
+    def service_reload(self, service_name, restart_on_failure=False):
+        """Reload the specified service.
+
+        Meant to be overridden by child classes in scenarios where clustering
+        software like Pacemaker is used.
+
+        :param service_name: The service to reload.
+        :type service_name: str
+        """
+        ch_host.service_reload(service_name, restart_on_failure)
+
     @contextlib.contextmanager
     def restart_on_change(self):
         """Restart the services in the self.restart_map{} attribute if any of
@@ -704,16 +748,16 @@ class BaseOpenStackCharmActions(object):
                 restarts += self.full_restart_map[path]
         services_list = list(collections.OrderedDict.fromkeys(restarts).keys())
         for service_name in services_list:
-            ch_host.service_stop(service_name)
+            self.service_stop(service_name)
         for service_name in services_list:
-            ch_host.service_start(service_name)
+            self.service_start(service_name)
 
     def restart_all(self):
         """Restart all the services configured in the self.services[]
         attribute.
         """
         for svc in self.services:
-            ch_host.service_restart(svc)
+            self.service_restart(svc)
 
     def render_all_configs(self, adapters_instance=None):
         """Render (write) all of the config files identified as the keys in the

unit_tests/charms_openstack/charm/test_core.py

@@ -1066,3 +1066,23 @@ class TestMyOpenStackCharm(BaseOpenStackCharmTest):
         self.target.install.assert_called_once()
         self.target.remove_obsolete_packages.assert_called_once()
         self.target.restart_all.assert_not_called()
+
+    def test_service_stop(self):
+        self.patch_object(chm_core.ch_host, 'service_stop')
+        self.target.service_stop('test-svc')
+        self.service_stop.assert_called_once_with('test-svc')
+
+    def test_service_start(self):
+        self.patch_object(chm_core.ch_host, 'service_start')
+        self.target.service_start('test-svc')
+        self.service_start.assert_called_once_with('test-svc')
+
+    def test_service_restart(self):
+        self.patch_object(chm_core.ch_host, 'service_restart')
+        self.target.service_restart('test-svc')
+        self.service_restart.assert_called_once_with('test-svc')
+
+    def test_service_reload(self):
+        self.patch_object(chm_core.ch_host, 'service_reload')
+        self.target.service_reload('test-svc')
+        self.service_reload.assert_called_once_with('test-svc', False)