Fix persistent config file not update bug

When ceph doing the version upgrade, it will check the previous ceph
from the `source` config variable which store in persistent file.
But the persistent file update is broken. It is because we use hookenv.Config
from ops framework, but the hookenv._run_atexit, which
save the change to file, is not been called.

Partial-Bug: #2007976
Change-Id: Ibf12a2b87736cb1d32788672fb390e027f15b936
func-test-pr: https://github.com/openstack-charmers/zaza-openstack-tests/pull/1047

src/charm.py

@@ -157,6 +157,13 @@ class CephMonCharm(ops_openstack.core.OSBaseCharm):
     def on_commit(self, _event):
         self.ceph_status.assess_status()
 
+    def on_pre_commit(self, _event):
+        # Fix bug: https://bugs.launchpad.net/charm-ceph-mon/+bug/2007976
+        # The persistent config file doesn't update because the config save
+        # function handled by atexit is not triggered.
+        # Trigger it manually here.
+        hooks.hookenv._run_atexit()
+
     # Actions.
 
     def _observe_action(self, on_action, callable):
@@ -273,6 +280,8 @@ class CephMonCharm(ops_openstack.core.OSBaseCharm):
 
         fw.observe(self.on.notify_clients, self.notify_clients)
 
+        fw.observe(self.on.framework.on.pre_commit, self.on_pre_commit)
+
     def ready_for_service(self):
         return hooks.ready_for_service()
 

tests/tests.yaml

@@ -26,6 +26,7 @@ tests:
   - zaza.openstack.charm_tests.ceph.tests.CephPrometheusTest
   # Charm upgrade, then re-run tests
   - zaza.charm_tests.lifecycle.tests.UpgradeCharmsToPath;ceph-mon
+  - zaza.openstack.charm_tests.ceph.tests.CephMonJujuPersistent
   - zaza.openstack.charm_tests.ceph.tests.CheckPoolTypes
   - zaza.openstack.charm_tests.ceph.tests.CephLowLevelTest
   - zaza.openstack.charm_tests.ceph.tests.CephTest

unit_tests/test_charm.py

@@ -63,3 +63,8 @@ class TestCephCharm(unittest.TestCase):
             fatal=True,
         )
         apt_update.assert_called()
+
+    @patch("charm.hooks")
+    def test_on_pre_commit(self, hooks):
+        self.harness.charm.on.framework.on.pre_commit.emit()
+        hooks.hookenv._run_atexit.assert_called()