add first draft of pseudo code for data plane upgrade

cou/apps/base.py

@@ -58,6 +58,16 @@ class ApplicationUnit:
     machine: str = ""
 
 
+@dataclass
+class ApplicationMachine:
+    """Representation of single machine of application."""
+
+    id: str
+    hostname: str
+    az: str
+    apps: list[OpenStackApplication]
+
+
 @dataclass
 class OpenStackApplication:
     """Representation of a charmed OpenStack application in the deployment.
@@ -83,6 +93,12 @@ class OpenStackApplication:
     :type channel: str, defaults to ""
     :param units: Units representation of an application.
     :type units: list[ApplicationUnit]
+    :param machines: Machines representation of an application.
+    :type machines: list[ApplicationMachine]
+    :param wait_timeout: Waiting time for application/model status
+    :type wait_timeout: int
+    :param wait_for_model: Wait for app itself or for all OpenStack related applications
+    :type wait_for_model: bool
     :raises ApplicationError: When there are no compatible OpenStack release for the
         workload version.
     :raises MismatchedOpenStackVersions: When units part of this application are running mismatched
@@ -173,6 +189,11 @@ def _populate_units(self) -> None:
                     )
                 )
 
+    @property
+    def is_data_plane(self) -> bool:
+        """Check if applications belong to data plane."""
+        raise NotImplementedError
+
     @property
     def is_subordinate(self) -> bool:
         """Check if application is subordinate.
@@ -225,6 +246,11 @@ def is_from_charm_store(self) -> bool:
         """
         return self.charm_origin == "cs"
 
+    @property
+    def machines(self) -> list[ApplicationMachine]:
+        """Return list of machines."""
+        raise NotImplementedError
+
     def is_valid_track(self, charm_channel: str) -> bool:
         """Check if the channel track is valid.
 
@@ -390,6 +416,17 @@ def can_upgrade_current_channel(self) -> bool:
         """
         return bool(self.status.can_upgrade_to)
 
+    async def populate_units(self) -> None:
+        """Populate units and filtered them.
+
+        This function is responsible for configuring the units for the application and at the same
+        time filtering them. e.g. Use only the machines that are required by user.
+
+        In specific applications such as nova-compute, it can be used to filter out non-empty
+        hypervisors.
+        """
+        raise NotImplementedError
+
     def new_origin(self, target: OpenStackRelease) -> str:
         """Return the new openstack-origin or source configuration.
 

cou/apps/data_plane.py

@@ -0,0 +1,72 @@
+# Copyright 2024 Canonical Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Data plane application class."""
+import logging
+from typing import Optional
+
+from cou.apps.base import OpenStackApplication
+from cou.apps.factory import AppFactory
+
+logger = logging.getLogger(__name__)
+
+
+class BaseDataPlaneApplication(OpenStackApplication):
+    """Base data plane application."""
+
+    async def _check_control_plane_was_upgraded(self) -> bool:
+        """Check that all control plane apps was upgraded.
+
+        This function is part of required pre-checks for all data plane apps.
+        """
+        raise NotImplementedError
+
+    async def populate_units(
+        self,
+        hostname: Optional[str] = None,
+        machine_id: Optional[str] = None,
+        az: Optional[str] = None,
+    ) -> None:
+        """Populate units and filtered specific machine, hostname or az.
+
+        :param hostname: machine hostname
+        :type hostname: str
+        :param machine_id: machine id
+        :type machine_id: str
+        :param az: az of machine
+        :type az: str
+        """
+        raise NotImplementedError
+
+
+@AppFactory.register_application(["nova-compute"])
+class NovaCompute(BaseDataPlaneApplication):
+    """Nova-compute application."""
+
+    wait_timeout = 30 * 60  # 30 min
+    wait_for_model = True
+
+    async def instance_count(self) -> int:
+        """Get number of instances running on hypervisor."""
+        raise NotImplementedError
+
+    async def populate_units(self, *args: Optional[str], **kwargs: Optional[str]) -> None:
+        """Populate units and filtered specific machine, hostname or az.
+
+        :param args: arguments parser
+        :type args: Any
+        :param kwargs: named argument parser
+        :type kwargs: Any
+        """
+        raise NotImplementedError

cou/steps/analyze.py

@@ -55,14 +55,23 @@ def __post_init__(self) -> None:
         self.current_cloud_os_release = self._get_minimum_cloud_os_release()
         self.current_cloud_series = self._get_minimum_cloud_series()
 
+    @staticmethod
+    def _sort_apps(apps: list[OpenStackApplication]) -> list[OpenStackApplication]:
+        """Sort apps in order relevant to upgrade.
+
+        :param apps: List of applications to split.
+        :type apps: list[OpenStackApplication]
+        """
+        raise NotImplementedError
+
     @staticmethod
     def _split_apps(
         apps: list[OpenStackApplication],
     ) -> tuple[list[OpenStackApplication], list[OpenStackApplication]]:
         """Split applications to control plane and data plane apps.
 
         :param apps: List of applications to split.
-        :type apps: Iterable[OpenStackApplication]
+        :type apps: list[OpenStackApplication]
         :return: Control plane and data plane application lists.
         :rtype: tuple[list[OpenStackApplication], list[OpenStackApplication]]
         """

pyproject.toml

@@ -50,6 +50,9 @@ ignore-paths = [
     "tests",
     "docs"
 ]
+disable = [
+    "W0223",
+]
 no-docstring-rgx = "__.*__"
 default-docstring-type = "sphinx"
 accept-no-param-doc = false
@@ -80,11 +83,14 @@ exclude = [
 relative_files = true
 concurrency = ["gevent"]
 source = ["."]
-omit = ["tests/**", "docs/**", "lib/**", "snap/**", "build/**", "setup.py"]
+omit = ["tests/**", "docs/**", "lib/**", "snap/**", "build/**", "setup.py", "cou/apps/data_plane.py"]
 
 [tool.coverage.report]
 fail_under = 100
 show_missing = true
+exclude_also = [
+    "raise NotImplementedError"
+]
 
 [tool.coverage.html]
 directory = "tests/unit/report/html"