Check possible charm downgrade when upgrading the channel (#392)

- changed from `channel_codename` to `current_channel_os_release` to
represent the OpenStack release that the charm channel points to
- added `from` to` to be more explicit about the charm channel upgrade
- changed abbreviation of OpenStack from `os` to `o7k`
 
Closes: #376

cou/apps/auxiliary.py

@@ -49,13 +49,9 @@ def is_valid_track(self, charm_channel: str) -> bool:
         :return: True if valid, False otherwise.
         :rtype: bool
         """
-        if self.is_from_charm_store:
-            logger.debug("'%s' has been installed from the charm store", self.name)
-            return True
-
         current_track = self._get_track_from_channel(charm_channel)
         possible_tracks = OPENSTACK_TO_TRACK_MAPPING.get(
-            (self.charm, self.series, self.current_os_release.codename), []
+            (self.charm, self.series, self.o7k_release.codename), []
         )
         return (
             self.charm,
@@ -81,7 +77,7 @@ def expected_current_channel(self, target: OpenStackRelease) -> str:
             ]
         else:
             *_, track = OPENSTACK_TO_TRACK_MAPPING[
-                (self.charm, self.series, self.current_os_release.codename)
+                (self.charm, self.series, self.o7k_release.codename)
             ]
 
         return f"{track}/stable"
@@ -107,37 +103,30 @@ def target_channel(self, target: OpenStackRelease) -> str:
             )
         )
 
-    @property
-    def channel_codename(self) -> OpenStackRelease:
-        """Identify the OpenStack release set in the charm channel.
+    def _get_o7k_release_from_channel(self, channel: str) -> OpenStackRelease:
+        """Get the OpenStack release from a channel.
 
-        Auxiliary charms can have multiple compatible OpenStack releases. In
-        that case, return the latest compatible OpenStack version.
+        Auxiliary charms can have multiple compatible OpenStack releases. In that case, return the
+        latest compatible OpenStack version.
 
-        :return: OpenStackRelease object
+        :param channel: channel to get the release
+        :type channel: str
+        :return: OpenStack release that the channel points to
         :rtype: OpenStackRelease
         :raises ApplicationError: When cannot identify suitable OpenStack release codename
-                                  based on the track of the charm channel.
         """
-        if self.need_crossgrade:
-            logger.debug(
-                "Cannot determine the OpenStack release of '%s' via its channel. Assuming Ussuri",
-                self.name,
-            )
-            return OpenStackRelease("ussuri")
-
-        track: str = self._get_track_from_channel(self.channel)
-        compatible_os_releases = TRACK_TO_OPENSTACK_MAPPING[(self.charm, self.series, track)]
+        track: str = self._get_track_from_channel(channel)
+        compatible_o7k_releases = TRACK_TO_OPENSTACK_MAPPING[(self.charm, self.series, track)]
 
-        if not compatible_os_releases:
+        if not compatible_o7k_releases:
             raise ApplicationError(
                 f"Channel: {self.channel} for charm '{self.charm}' on series '{self.series}' is "
                 f"not supported by COU. Please take a look at the documentation: "
                 "https://docs.openstack.org/charm-guide/latest/project/charm-delivery.html to see "
                 "if you are using the right track."
             )
 
-        return max(compatible_os_releases)
+        return max(compatible_o7k_releases)
 
     def generate_upgrade_plan(
         self,
@@ -175,9 +164,9 @@ def _need_current_channel_refresh(self, target: OpenStackRelease) -> bool:
         :rtype: bool
         """
         track: str = self._get_track_from_channel(self.channel)
-        compatible_os_releases = TRACK_TO_OPENSTACK_MAPPING[(self.charm, self.series, track)]
+        compatible_o7k_releases = TRACK_TO_OPENSTACK_MAPPING[(self.charm, self.series, track)]
         return bool(self.can_upgrade_to) and any(
-            os_release <= target for os_release in compatible_os_releases
+            o7k_release <= target for o7k_release in compatible_o7k_releases
         )
 
 
@@ -357,11 +346,11 @@ async def _verify_nova_compute(self, target: OpenStackRelease) -> None:
                 continue
 
             for unit in app.units.values():
-                compatible_os_versions = OpenStackCodenameLookup.find_compatible_versions(
+                compatible_o7k_versions = OpenStackCodenameLookup.find_compatible_versions(
                     app.charm, unit.workload_version
                 )
 
-                if target not in compatible_os_versions:
+                if target not in compatible_o7k_versions:
                     units_not_upgraded.append(unit.name)
 
         if units_not_upgraded:

cou/apps/base.py

@@ -118,7 +118,7 @@ def __str__(self) -> str:
                         "name": unit.name,
                         "machine": unit.machine.machine_id,
                         "workload_version": unit.workload_version,
-                        "os_version": str(self.get_latest_os_version(unit)),
+                        "o7k_version": str(self.get_latest_o7k_version(unit)),
                     }
                     for unit in self.units.values()
                 },
@@ -152,19 +152,19 @@ def apt_source_codename(self) -> OpenStackRelease:
         :rtype: OpenStackRelease
         """
         #  means that the charm doesn't have origin setting config or is using empty string.
-        if not self.os_origin:
-            return self.current_os_release
+        if not self.o7k_origin:
+            return self.o7k_release
 
-        if self.os_origin.startswith("cloud"):
+        if self.o7k_origin.startswith("cloud"):
             return self._extract_from_uca_source()
 
-        if self.os_origin == "distro":
+        if self.o7k_origin == "distro":
             # find the OpenStack release based on ubuntu series
             return OpenStackRelease(DISTRO_TO_OPENSTACK_MAPPING[self.series])
 
         # probably because user set a ppa or a url
         raise ApplicationError(
-            f"'{self.name}' has an invalid '{self.origin_setting}': {self.os_origin}"
+            f"'{self.name}' has an invalid '{self.origin_setting}': {self.o7k_origin}"
         )
 
     def _extract_from_uca_source(self) -> OpenStackRelease:
@@ -176,15 +176,15 @@ def _extract_from_uca_source(self) -> OpenStackRelease:
         """
         # Ex: "cloud:focal-victoria" will result in "victoria"
         try:
-            _, os_origin_parsed = self.os_origin.rsplit("-", maxsplit=1)
-            return OpenStackRelease(os_origin_parsed)
+            _, o7k_origin_parsed = self.o7k_origin.rsplit("-", maxsplit=1)
+            return OpenStackRelease(o7k_origin_parsed)
         except ValueError as exc:
             raise ApplicationError(
-                f"'{self.name}' has an invalid '{self.origin_setting}': {self.os_origin}"
+                f"'{self.name}' has an invalid '{self.origin_setting}': {self.o7k_origin}"
             ) from exc
 
     @property
-    def channel_codename(self) -> OpenStackRelease:
+    def channel_o7k_release(self) -> OpenStackRelease:
         """Identify the OpenStack release set in the charm channel.
 
         :return: OpenStackRelease object
@@ -197,21 +197,29 @@ def channel_codename(self) -> OpenStackRelease:
                 self.name,
             )
             return OpenStackRelease("ussuri")
+        return self._get_o7k_release_from_channel(self.channel)
 
-        # get the OpenStack release from the channel track of the application.
-        return OpenStackRelease(self._get_track_from_channel(self.channel))
+    def _get_o7k_release_from_channel(self, channel: str) -> OpenStackRelease:
+        """Get the OpenStack release from a channel.
+
+        :param channel: channel to get the release
+        :type channel: str
+        :return: OpenStack release that the channel points to
+        :rtype: OpenStackRelease
+        """
+        return OpenStackRelease(self._get_track_from_channel(channel))
 
     @property
-    def current_os_release(self) -> OpenStackRelease:
+    def o7k_release(self) -> OpenStackRelease:
         """Current OpenStack Release of the application.
 
         :return: OpenStackRelease object
         :rtype: OpenStackRelease
         """
-        return min(self.os_release_units.keys())
+        return min(self.o7k_release_units.keys())
 
     @property
-    def os_origin(self) -> str:
+    def o7k_origin(self) -> str:
         """Get application configuration for openstack-origin or source.
 
         :return: Configuration parameter of the charm to set OpenStack origin.
@@ -251,21 +259,21 @@ def expected_current_channel(self, target: OpenStackRelease) -> str:
         """
         if self.need_crossgrade and self.based_on_channel:
             return f"{target.previous_release}/stable"
-        return f"{self.current_os_release}/stable"
+        return f"{self.o7k_release}/stable"
 
     @property
-    def os_release_units(self) -> dict[OpenStackRelease, list[str]]:
+    def o7k_release_units(self) -> dict[OpenStackRelease, list[str]]:
         """Get the OpenStack release versions from the units.
 
         :return: OpenStack release versions from the units.
         :rtype: defaultdict[OpenStackRelease, list[str]]
         """
-        os_versions = defaultdict(list)
+        o7k_versions = defaultdict(list)
         for unit in self.units.values():
-            os_version = self.get_latest_os_version(unit)
-            os_versions[os_version].append(unit.name)
+            o7k_version = self.get_latest_o7k_version(unit)
+            o7k_versions[o7k_version].append(unit.name)
 
-        return dict(os_versions)
+        return dict(o7k_versions)
 
     @property
     def need_crossgrade(self) -> bool:
@@ -290,7 +298,7 @@ def is_valid_track(self, charm_channel: str) -> bool:
         except ValueError:
             return False
 
-    def get_latest_os_version(self, unit: Unit) -> OpenStackRelease:
+    def get_latest_o7k_version(self, unit: Unit) -> OpenStackRelease:
         """Get the latest compatible OpenStack release based on the unit workload version.
 
         :param unit: Unit
@@ -300,16 +308,16 @@ def get_latest_os_version(self, unit: Unit) -> OpenStackRelease:
         :raises ApplicationError: When there are no compatible OpenStack release for the
                                   workload version.
         """
-        compatible_os_versions = OpenStackCodenameLookup.find_compatible_versions(
+        compatible_o7k_versions = OpenStackCodenameLookup.find_compatible_versions(
             self.charm, unit.workload_version
         )
-        if not compatible_os_versions:
+        if not compatible_o7k_versions:
             raise ApplicationError(
                 f"'{self.name}' with workload version {unit.workload_version} has no "
                 "compatible OpenStack release."
             )
 
-        return max(compatible_os_versions)
+        return max(compatible_o7k_versions)
 
     @staticmethod
     def _get_track_from_channel(charm_channel: str) -> str:
@@ -361,10 +369,10 @@ async def _verify_workload_upgrade(self, target: OpenStackRelease, units: list[U
         units_not_upgraded = []
         for unit in units:
             workload_version = app_status.units[unit.name].workload_version
-            compatible_os_versions = OpenStackCodenameLookup.find_compatible_versions(
+            compatible_o7k_versions = OpenStackCodenameLookup.find_compatible_versions(
                 self.charm, workload_version
             )
-            if target not in compatible_os_versions:
+            if target not in compatible_o7k_versions:
                 units_not_upgraded.append(unit.name)
 
         if units_not_upgraded:
@@ -556,7 +564,10 @@ def _get_refresh_charm_step(self, target: OpenStackRelease) -> PreUpgradeStep:
         if self.is_from_charm_store:
             return self._get_charmhub_migration_step(target)
         if self.channel == LATEST_STABLE:
-            return self._get_change_to_openstack_channels_step(target)
+            return self._get_change_channel_possible_downgrade_step(
+                target, self.expected_current_channel(target)
+            )
+
         if self._need_current_channel_refresh(target):
             return self._get_refresh_current_channel_step()
         logger.info(
@@ -579,27 +590,32 @@ def _get_charmhub_migration_step(self, target: OpenStackRelease) -> PreUpgradeSt
             ),
         )
 
-    def _get_change_to_openstack_channels_step(self, target: OpenStackRelease) -> PreUpgradeStep:
-        """Get the step for changing to an OpenStack channel.
+    def _get_change_channel_possible_downgrade_step(
+        self, target: OpenStackRelease, channel: str
+    ) -> PreUpgradeStep:
+        """Get the step for changing to a channel that can be a downgrade.
 
-        :param target: OpenStack release as target to upgrade.
+        :param target:  OpenStack release as target to upgrade
         :type target: OpenStackRelease
-        :return: Step for changing to OpenStack channels
+        :param channel: channel to upgrade
+        :type channel: str
+        :return:  Step for possible downgrade.
         :rtype: PreUpgradeStep
         """
         logger.warning(
             "Changing '%s' channel from %s to %s to upgrade to %s. This may be a charm downgrade, "
             "which is generally not supported.",
             self.name,
             self.channel,
-            self.expected_current_channel(target),
+            channel,
             target,
         )
-        return PreUpgradeStep(
+        description = (
             f"WARNING: Changing '{self.name}' channel from {self.channel} to "
-            f"{self.expected_current_channel(target)}. This may be a charm downgrade, "
-            "which is generally not supported.",
-            coro=self.model.upgrade_charm(self.name, self.expected_current_channel(target)),
+            f"{channel}. This may be a charm downgrade, which is generally not supported."
+        )
+        return PreUpgradeStep(
+            description=description, coro=self.model.upgrade_charm(self.name, channel)
         )
 
     def _get_refresh_current_channel_step(self) -> PreUpgradeStep:
@@ -621,23 +637,38 @@ def _need_current_channel_refresh(self, target: OpenStackRelease) -> bool:
         :return: True if needs to refresh, False otherwise
         :rtype: bool
         """
-        return bool(self.can_upgrade_to) and self.channel_codename <= target
+        return bool(self.can_upgrade_to) and self.channel_o7k_release <= target
 
     def _get_upgrade_charm_step(self, target: OpenStackRelease) -> UpgradeStep:
         """Get step for upgrading the charm.
 
         :param target: OpenStack release as target to upgrade.
         :type target: OpenStackRelease
+        :raises ApplicationError: When the current channel is ahead from expected and the target.
         :return: Step for upgrading the charm.
         :rtype: UpgradeStep
         """
-        if self.channel != self.target_channel(target):
+        channel = self.expected_current_channel(target) if self.need_crossgrade else self.channel
+
+        if channel == self.target_channel(target):
+            logger.debug("%s channel already set to %s", self.name, self.channel)
+            return UpgradeStep()
+
+        # Normally, prior the upgrade the channel is equal to the application release.
+        # However, when colocated with other app, the channel can be in a release lesser than the
+        # workload version of the application.
+        if self.channel_o7k_release <= self.o7k_release:
             return UpgradeStep(
-                description=f"Upgrade '{self.name}' to the new channel: "
+                description=f"Upgrade '{self.name}' from '{channel}' to the new channel: "
                 f"'{self.target_channel(target)}'",
                 coro=self.model.upgrade_charm(self.name, self.target_channel(target)),
             )
-        return UpgradeStep()
+
+        raise ApplicationError(
+            f"The '{self.name}' application is using channel '{self.channel}'. Channels supported "
+            f"during this transition: '{self.expected_current_channel(target)}', "
+            f"'{self.target_channel(target)}'. Manual intervention is required."
+        )
 
     def _set_action_managed_upgrade(self, enable: bool) -> UpgradeStep:
         """Set action-managed-upgrade config option.
@@ -724,7 +755,7 @@ def _get_change_install_repository_step(self, target: OpenStackRelease) -> Upgra
         :return: Workload upgrade step
         :rtype: UpgradeStep
         """
-        if self.os_origin != self.new_origin(target) and self.origin_setting:
+        if self.o7k_origin != self.new_origin(target) and self.origin_setting:
             return UpgradeStep(
                 f"Change charm config of '{self.name}' '{self.origin_setting}' to "
                 f"'{self.new_origin(target)}'",
@@ -830,14 +861,14 @@ def _check_application_target(self, target: OpenStackRelease) -> None:
         :raises HaltUpgradePlanGeneration: When the application halt the upgrade plan generation.
         """
         logger.debug(
-            "%s application current os_release is %s and apt source is %s",
+            "%s application current o7k_release is %s and apt source is %s",
             self.name,
-            self.current_os_release,
+            self.o7k_release,
             self.apt_source_codename,
         )
 
         if (
-            self.current_os_release >= target
+            self.o7k_release >= target
             and not self.can_upgrade_to
             and self.apt_source_codename >= target
         ):
@@ -867,11 +898,11 @@ def _check_mismatched_versions(self, units: Optional[list[Unit]]) -> None:
         ):
             return
 
-        os_versions = self.os_release_units
-        if len(os_versions.keys()) > 1:
+        o7k_versions = self.o7k_release_units
+        if len(o7k_versions.keys()) > 1:
             mismatched_repr = [
                 f"'{openstack_release.codename}': {units}"
-                for openstack_release, units in os_versions.items()
+                for openstack_release, units in o7k_versions.items()
             ]
 
             raise MismatchedOpenStackVersions(