Fix removal of designate-agent package in caracal

In the current implementation, the charm instance
i.e., DesignateCharm<*> passes a release name based
on python-keystonemiddleware package. However the
internal logic ignores the package and installs
openstack-release package and determines the release
and creates singleton class for that release. The
singelton class determines the list of packages etc.
However at this point of time, the cloud-archive source
is not yet updated.

In case of jammy-caracal deployment, the openstack-release
package is installed from jammy since the cloud archive source
is not updated and hence openstack release is considered as
yoga. This means packages listed in DesignateCharmYoga will
be installed that includes designate-agent. After running some
handlers, configure_designate_full crosschecks the packages
with openstack-origin configuration and starts upgrading the
packages to caracal. There are no purge_packages listed in
CharmDesignateCaracal and so designate-agent is not removed
during this upgrade.

Do not pass any release so that charms.openstack library figures
out the release name after updating the cloud-archive sources.
This should fix issues for a greenfield deployment.

For the case of upgrades from earlier releases where
designate-agent is already installed, update purge packages in
CharmDesignateCaracal. To remove/purge nrpe service check, add
logic to trigger remove_deperecated_packages.
There is a case where designate-agent gets purged and reinstalled
due to the way hooks are triggered and singleton class is
maintained. To overcome this, always remove_obselete_packages
in configure_designate_full handler.

Closes-Bug: #2111227
Change-Id: I9f8ce93b9751a65e8e181cf9aa7411a4047318bb

src/lib/charm/openstack/designate.py

@@ -315,6 +315,8 @@ class DesignateCharm(ch_plugins.PolicydOverridePlugin,
                 'designate-central', 'designate-sink',
                 'designate-api']
 
+    deprecated_services = []
+
     api_ports = {
         'designate-api': {
             os_ip.PUBLIC: 9001,
@@ -370,15 +372,6 @@ class DesignateCharm(ch_plugins.PolicydOverridePlugin,
     # policyd override constants
     policyd_service_name = 'designate'
 
-    def __init__(self, release=None, **kwargs):
-        """Custom initialiser for class
-        If no release is passed, then the charm determines the release from the
-        ch_utils.os_release() function.
-        """
-        if release is None:
-            release = ch_utils.os_release('python-keystonemiddleware')
-        super(DesignateCharm, self).__init__(release=release, **kwargs)
-
     def install(self):
         """Customise the installation, configure the source and then call the
         parent install() method to install the packages
@@ -657,6 +650,8 @@ class DesignateCharm(ch_plugins.PolicydOverridePlugin,
         nrpe.add_init_service_checks(
             charm_nrpe, self.services, current_unit)
         charm_nrpe.write()
+        # Remove service checks for which services are no longer needed
+        nrpe.remove_deprecated_check(charm_nrpe, self.deprecated_services)
 
     def add_nrpe_nameserver_checks(self):
         """Add NRPE service checks for upstream nameservers."""
@@ -804,7 +799,17 @@ class DesignateCharmCaracal(DesignateCharmRocky):
                 'python3-designate',
                 'python3-apt']
 
+    purge_packages = [
+        'python-designate',
+        'python-memcache',
+        'designate-agent',
+        'designate-zone-manager',
+        'designate-pool-manager',
+    ]
+
     services = ['designate-mdns', 'designate-producer',
                 'designate-worker',
                 'designate-central', 'designate-sink',
                 'designate-api']
+
+    deprecated_services = ["designate-agent"]

src/reactive/designate_handlers.py

@@ -210,6 +210,19 @@ def configure_designate_full(*args):
         args = args + (dns_backend, )
     with charm.provide_charm_instance() as instance:
         instance.upgrade_if_available(args)
+        # Workaround to purge packages in case of upgrades from one release to
+        # another
+        # Eventhough upgrade_if_available() purges the unnecessary packages,
+        # reactive/layer_openstack.py::default_upgrade_charm again tries to
+        # install due to singleton class pointing to older release charm
+        # instance i.e., it installs all the packages mentioned in older
+        # release. After that even though configure_designate_full() is
+        # triggered, upgrade_if_available does nothing as the installed
+        # packages are already of same release as expected and it
+        # did not care about purge packages.
+        # Example scenario that triggered this change is removal of
+        # designate-agent from caracal release
+        instance.remove_obsolete_packages()
         instance.configure_ssl()
         instance.render_full_config(args)
         try:

unit_tests/test_designate_handlers.py

@@ -221,6 +221,7 @@ class TestHandlers(test_utils.PatchHelper):
         the_charm.update_pools.assert_called_once_with()
         the_charm.upgrade_if_available.assert_called_once_with(
             ('arg1', 'arg2', ))
+        the_charm.remove_obsolete_packages.assert_called_once_with()
 
     def test_cluster_connected(self):
         the_charm = self._patch_provide_charm_instance()