Publish releases packages map to principal charm

For principal - subordinate plugin type relations where the
principal Python payload imports code from packages managed by a
subordinate, upgrades can be problematic.

This change will allow a subordinate charm that have opted into the
feature to inform its principal about all implemented release -
packages combinations ahead of time. With this information in place
the principal can do the upgrade in one operation without risk of
charm relation RPC type processing at a critical moment.

This is similar to
https://review.opendev.org/c/openstack/charm-interface-keystone-domain-backend/+/781658
https://review.opendev.org/c/openstack/charm-layer-openstack/+/781624

Change-Id: Ibd5bdcb141fc3103ee97123ff284fb2957802eba
Closes-Bug: #1927277

hooks/ceilometer_hooks.py

@@ -59,6 +59,7 @@ from ceilometer_utils import (
     NOVA_SETTINGS,
     assess_status,
     get_packages,
+    releases_packages_map,
     pause_unit_helper,
     resume_unit_helper,
     remove_old_packages,
@@ -83,8 +84,14 @@ def install():
 
 @hooks.hook('nova-ceilometer-relation-joined')
 def nova_ceilometer_joined(relation_id=None):
-    relation_set(relation_id=relation_id,
-                 subordinate_configuration=json.dumps(NOVA_SETTINGS))
+    relation_set(
+        relation_id=relation_id,
+        relation_settings={
+            'subordinate_configuration': json.dumps(NOVA_SETTINGS),
+            'releases-packages-map': json.dumps(
+                releases_packages_map(), sort_keys=True),
+            'services': json.dumps(services())
+        })
 
 
 @hooks.hook("ceilometer-service-relation-changed")

hooks/ceilometer_utils.py

@@ -115,8 +115,7 @@ def register_configs():
     # if called without anything installed (eg during install hook)
     # just default to earliest supported release. configs dont get touched
     # till post-install, anyway.
-    release = get_os_codename_package('ceilometer-common', fatal=False) \
-        or 'icehouse'
+    release = _get_current_release()
     configs = templating.OSConfigRenderer(templates_dir=TEMPLATES,
                                           openstack_release=release)
 
@@ -137,8 +136,7 @@ def register_configs():
 
 
 def get_packages():
-    release = CompareOpenStackReleases(get_os_codename_package(
-        'ceilometer-common', fatal=False) or 'icehouse')
+    release = _get_current_release()
 
     packages = deepcopy(CEILOMETER_AGENT_PACKAGES)
     packages.extend(token_cache_pkgs(release=release))
@@ -157,8 +155,7 @@ def determine_purge_packages():
 
     :returns: list of package names
     '''
-    release = CompareOpenStackReleases(get_os_codename_package(
-        'ceilometer-common', fatal=False) or 'icehouse')
+    release = _get_current_release()
     if release >= 'rocky':
         pkgs = [p for p in CEILOMETER_AGENT_PACKAGES
                 if p.startswith('python-')]
@@ -166,6 +163,40 @@ def determine_purge_packages():
     return []
 
 
+def releases_packages_map():
+    '''Provide a map of all supported releases and their packages.
+
+    NOTE(lourot): this is a simplified version of a more generic
+    implementation:
+    https://github.com/openstack/charms.openstack/blob/master/charms_openstack/charm/core.py
+
+    :returns: Map of release, package type and install / purge packages.
+        Example:
+        {
+            'mitaka': {
+                'deb': {
+                    'install': ['python-ldappool'],
+                    'purge': []
+                }
+            },
+            'rocky': {
+                'deb': {
+                    'install': ['python3-ldap', 'python3-ldappool'],
+                    'purge': ['python-ldap', 'python-ldappool']}
+            }
+        }
+    :rtype: Dict[str,Dict[str,List[str]]]
+    '''
+    return {
+        _get_current_release(): {
+            'deb': {
+                'install': get_packages(),
+                'purge': determine_purge_packages(),
+            }
+        }
+    }
+
+
 def remove_old_packages():
     '''Purge any packages that need ot be removed.
 
@@ -183,8 +214,7 @@ def remove_old_packages():
 def determine_held_packages():
     '''Return a list of packages to mark as candidates for removal
     for the current OS release'''
-    release = CompareOpenStackReleases(get_os_codename_package(
-        'ceilometer-common', fatal=False) or 'icehouse')
+    release = _get_current_release()
     if release >= 'rocky':
         return HELD_PACKAGES
     return []
@@ -198,8 +228,7 @@ def restart_map():
     :returns: dict: A dictionary mapping config file to lists of services
                     that should be restarted when file changes.
     '''
-    release = (get_os_codename_package('ceilometer-common', fatal=False) or
-               'icehouse')
+    release = _get_current_release()
 
     if CompareOpenStackReleases(release) >= 'queens':
         _config_files = QUEENS_CONFIG_FILES
@@ -291,3 +320,8 @@ def _pause_resume_helper(f, configs):
     f(assess_status_func(configs),
       services=services(),
       ports=None)
+
+
+def _get_current_release():
+    return (get_os_codename_package('ceilometer-common', fatal=False)
+            or 'icehouse')

unit_tests/test_ceilometer_hooks.py

@@ -29,6 +29,8 @@ TO_PATCH = [
     'apt_update',
     'filter_installed_packages',
     'get_packages',
+    'releases_packages_map',
+    'services',
     'is_relation_made',
     'is_unit_paused_set',
     'relation_set',
@@ -65,11 +67,27 @@ class CeilometerHooksTest(CharmTestCase):
 
     @patch('charmhelpers.core.hookenv.config')
     def test_nova_ceilometer_joined(self, mock_config):
+        mocked_releases_packages_map = {
+            'ussuri': {
+                'deb': {
+                    'install': [
+                        'ceilometer-common', 'ceilometer-agent-compute',
+                        'python3-ceilometer', 'python3-memcache'],
+                    'purge': ['python-ceilometer'],
+                }}}
+        mocked_services = ['ceilometer-agent-compute']
+
+        self.releases_packages_map.return_value = mocked_releases_packages_map
+        self.services.return_value = mocked_services
         hooks.hooks.execute(['hooks/nova-ceilometer-relation-joined'])
         self.relation_set.assert_called_with(
             relation_id=None,
-            subordinate_configuration=json.dumps(
-                ceilometer_utils.NOVA_SETTINGS))
+            relation_settings={
+                'subordinate_configuration': json.dumps(
+                    ceilometer_utils.NOVA_SETTINGS),
+                'releases-packages-map': json.dumps(
+                    mocked_releases_packages_map, sort_keys=True),
+                'services': json.dumps(mocked_services)})
 
     @patch('charmhelpers.core.hookenv.config')
     def test_config_changed(self, mock_config):

unit_tests/test_ceilometer_utils.py

@@ -157,3 +157,15 @@ class CeilometerUtilsTest(CharmTestCase):
                          sorted([p for p in utils.CEILOMETER_AGENT_PACKAGES
                                  if not p.startswith('python-')] +
                                 ['python3-ceilometer', 'python3-memcache']))
+
+    def test_releases_packages_map(self):
+        self.get_os_codename_package.return_value = 'ussuri'
+        self.token_cache_pkgs.return_value = []
+        self.assertEqual(utils.releases_packages_map(), {
+            'ussuri': {
+                'deb': {
+                    'install': [
+                        'ceilometer-common', 'ceilometer-agent-compute',
+                        'python3-ceilometer', 'python3-memcache'],
+                    'purge': ['python-ceilometer'],
+                }}})