Deal with py2-py3 migration during charm upgrade

On charm upgrade the charm may switch to py3 packages. If so, ensure
the old py2 packages are purged after any new packages have been
installed.  If packages where removed during the upgrade, then
restart all services to pickup any py2->py3 switches.

Change-Id: I9acd536c437ff9d8c6a7056ac255aa4b6de62673
Closes-Bug: 1803451

hooks/heat_relations.py

@@ -42,6 +42,7 @@ from charmhelpers.core.host import (
     restart_on_change,
     service_reload,
     pwgen,
+    service_restart,
 )
 
 from charmhelpers.fetch import (
@@ -92,6 +93,8 @@ from heat_utils import (
     pause_unit_helper,
     resume_unit_helper,
     assess_status,
+    remove_old_packages,
+    services,
 )
 
 from heat_context import (
@@ -161,6 +164,11 @@ def config_changed():
 @hooks.hook('upgrade-charm')
 @harden()
 def upgrade_charm():
+    apt_install(determine_packages(), fatal=True)
+    if remove_old_packages():
+        log("Package purge detected, restarting services", "INFO")
+        for s in services():
+            service_restart(s)
     if is_leader():
         # if we are upgrading, then the old version might have used the
         # HEAT_PATH/encryption-key. So we grab the key from that, and put it in

hooks/heat_utils.py

@@ -232,6 +232,18 @@ def determine_purge_packages():
     return []
 
 
+def remove_old_packages():
+    '''Purge any packages that need ot be removed.
+
+    :returns: bool Whether packages were removed.
+    '''
+    installed_packages = filter_missing_packages(determine_purge_packages())
+    if installed_packages:
+        apt_purge(installed_packages, fatal=True)
+        apt_autoremove(purge=True, fatal=True)
+    return bool(installed_packages)
+
+
 def do_openstack_upgrade(configs):
     """Perform an uprade of heat.
 
@@ -256,10 +268,7 @@ def do_openstack_upgrade(configs):
     apt_upgrade(options=dpkg_opts, fatal=True, dist=True)
     apt_install(packages=determine_packages(), options=dpkg_opts, fatal=True)
 
-    installed_packages = filter_missing_packages(determine_purge_packages())
-    if installed_packages:
-        apt_purge(installed_packages, fatal=True)
-        apt_autoremove(purge=True, fatal=True)
+    remove_old_packages()
 
     # set CONFIGS to load templates from new release and regenerate config
     configs.set_release(openstack_release=new_os_rel)

unit_tests/test_heat_relations.py

@@ -55,6 +55,7 @@ TO_PATCH = [
     'apt_install',
     'apt_update',
     'restart_on_change',
+    'service_restart',
     # charmhelpers.contrib.openstack.utils
     'configure_installation_source',
     'openstack_upgrade_available',
@@ -68,6 +69,8 @@ TO_PATCH = [
     'restart_map',
     'register_configs',
     'do_openstack_upgrade',
+    'remove_old_packages',
+    'services',
     # other
     'execd_preinstall',
     'log',
@@ -133,12 +136,16 @@ class HeatRelationTests(CharmTestCase):
     def test_upgrade_charm(self, leader_elected, os_remove, os_path_isfile):
         os_path_isfile.return_value = False
         self.is_leader.return_value = False
+        self.remove_old_packages.return_value = True
+        self.services.return_value = ['heat-api']
+
         relations.upgrade_charm()
         leader_elected.assert_called_once_with()
         os_path_isfile.assert_not_called()
         # now say we are the leader
         self.is_leader.return_value = True
         os_path_isfile.return_value = False
+
         relations.upgrade_charm()
         self.leader_set.assert_not_called()
         os_path_isfile.return_value = True
@@ -150,6 +157,8 @@ class HeatRelationTests(CharmTestCase):
             self.leader_set.assert_called_once_with(
                 {'heat-auth-encryption-key': 'abc'})
             os_remove.assert_called_once_with(filename)
+        self.remove_old_packages.assert_called_with()
+        self.service_restart.assert_called_with('heat-api')
 
     def test_db_joined(self):
         self.get_relation_ip.return_value = '192.168.20.1'