Refactor custom status checks

Refactor custom status checks to allow the charm specific class and
the inherited general charm type classes to specify status checks.

Change-Id: Ib40fa3b46cc629d5b3e5b199a70cff22451661ee

ops_openstack/core.py

@@ -51,6 +51,7 @@ class OSBaseCharm(CharmBase):
 
     def __init__(self, framework):
         super().__init__(framework)
+        self.custom_status_checks = []
         self._stored.set_default(is_started=False)
         self._stored.set_default(is_paused=False)
         self._stored.set_default(series_upgrade=False)
@@ -79,15 +80,47 @@ class OSBaseCharm(CharmBase):
     def custom_status_check(self):
         raise NotImplementedError
 
+    def register_status_check(self, custom_check):
+        self.custom_status_checks.append(custom_check)
+
     def update_status(self):
+        """Update the charms status
+
+        A charm, or plugin, can register checks to be run when calculating the
+        charms status. Each status method should have a unique name. The custom
+        check should return a StatusBase object.  If the check returns an
+        ActiveStatus object then subsequent checks are run, if it returns
+        anything else then the charms status is set to the object the check
+        returned and no subsequent checks are run. If the check returns an
+        ActiveStatus with a specific message then this message will be
+        concatenated with the other active status messages.
+
+        Example::
+
+        class MyCharm(OSBaseCharm):
+
+            def __init__(self, framework):
+                super().__init__(framework)
+                super().register_status_check(self.mycharm_check)
+
+            def mycharm_check(self):
+                if self.model.config['plugin-check-fail'] == 'True':
+                    return BlockedStatus(
+                        'Plugin Custom check failed')
+                else:
+                    return ActiveStatus()
+
+        """
         logging.info("Updating status")
-        try:
+        active_messages = ['Unit is ready']
-            # Custom checks return True if the checked passed else False.
+        for check in self.custom_status_checks:
-            # If the check failed the custom check will have set the status.
+            _result = check()
-            if not self.custom_status_check():
+            if isinstance(_result, ActiveStatus):
+                if _result.message:
+                    active_messages.append(_result.message)
+            else:
+                self.unit.status = _result
                 return
-        except NotImplementedError:
-            pass
         if self._stored.series_upgrade:
             self.unit.status = BlockedStatus(
                 'Ready for do-release-upgrade and reboot. '
@@ -106,7 +139,16 @@ class OSBaseCharm(CharmBase):
                 'Missing relations: {}'.format(', '.join(missing_relations)))
             return
         if self._stored.is_started:
-            self.unit.status = ActiveStatus('Unit is ready')
+            _unique = []
+            # Reverse sort the list so that a shorter message that has the same
+            # start as a longer message comes first and can then be omitted.
+            # eg 'Unit is ready' comes after 'Unit is ready and clustered'
+            # and 'Unit is ready' is dropped.
+            for msg in sorted(list(set(active_messages)), reverse=True):
+                dupes = [m for m in _unique if m.startswith(msg)]
+                if not dupes:
+                    _unique.append(msg)
+            self.unit.status = ActiveStatus(', '.join(_unique))
         else:
             self.unit.status = WaitingStatus('Charm configuration in progress')
         logging.info("Status updated")

unit_tests/test_ops_openstack.py

@@ -29,7 +29,36 @@ from ops.model import (
 import ops_openstack.core
 
 
-class OpenStackTestAPICharm(ops_openstack.core.OSBaseCharm):
+class OpenStackTestPlugin1(ops_openstack.core.OSBaseCharm):
+
+    def __init__(self, framework):
+        super().__init__(framework)
+        super().register_status_check(self.plugin1_status_check)
+
+    def plugin1_status_check(self):
+        if self.model.config.get('plugin1-check-fail', 'False') == 'True':
+            return BlockedStatus(
+                'Plugin1 Custom check failed')
+        else:
+            return ActiveStatus('Unit is ready and awesome')
+
+
+class OpenStackTestPlugin2(ops_openstack.core.OSBaseCharm):
+
+    def __init__(self, framework):
+        super().__init__(framework)
+        super().register_status_check(self.plugin2_status_check)
+
+    def plugin2_status_check(self):
+        if self.model.config.get('plugin2-check-fail', 'False') == 'True':
+            return BlockedStatus(
+                'Plugin2 Custom check failed')
+        else:
+            return ActiveStatus('Unit is ready and super')
+
+
+class OpenStackTestAPICharm(OpenStackTestPlugin1,
+                            OpenStackTestPlugin2):
 
     PACKAGES = ['keystone-common']
     REQUIRED_RELATIONS = ['shared-db']
@@ -38,13 +67,15 @@ class OpenStackTestAPICharm(ops_openstack.core.OSBaseCharm):
         '/etc/f2.conf': ['apache2', 'ks-api'],
         '/etc/f3.conf': []}
 
+    def __init__(self, framework):
+        super().__init__(framework)
+        super().register_status_check(self.custom_status_check)
+
     def custom_status_check(self):
         if self.model.config.get('custom-check-fail', 'False') == 'True':
-            self.unit.status = MaintenanceStatus(
+            return MaintenanceStatus('Custom check failed')
-                'Custom check failed')
-            return False
         else:
-            return True
+            return ActiveStatus()
 
 
 class CharmTestCase(unittest.TestCase):
@@ -131,7 +162,7 @@ class TestOSBaseCharm(CharmTestCase):
         self.harness.charm.on.update_status.emit()
         self.assertEqual(
             self.harness.charm.unit.status.message,
-            'Unit is ready')
+            'Unit is ready and super, Unit is ready and awesome')
         self.assertIsInstance(
             self.harness.charm.unit.status,
             ActiveStatus)
@@ -195,6 +226,33 @@ class TestOSBaseCharm(CharmTestCase):
             self.harness.charm.unit.status,
             BlockedStatus)
 
+    def test_update_status_plugin_check_fail(self):
+        self.harness.update_config(
+            key_values={
+                'plugin1-check-fail': 'True',
+                'plugin2-check-fail': 'False'})
+        self.harness.add_relation('shared-db', 'mysql')
+        self.harness.begin()
+        self.harness.charm._stored.is_started = True
+        self.harness.charm.on.update_status.emit()
+        self.assertEqual(
+            self.harness.charm.unit.status.message,
+            'Plugin1 Custom check failed')
+        self.assertIsInstance(
+            self.harness.charm.unit.status,
+            BlockedStatus)
+        self.harness.update_config(
+            key_values={
+                'plugin1-check-fail': 'False',
+                'plugin2-check-fail': 'True'})
+        self.harness.charm.on.update_status.emit()
+        self.assertEqual(
+            self.harness.charm.unit.status.message,
+            'Plugin2 Custom check failed')
+        self.assertIsInstance(
+            self.harness.charm.unit.status,
+            BlockedStatus)
+
     def test_services(self):
         self.harness.begin()
         self.assertEqual(