feat: enable juju-systemd-notices to observe snap services (#128)

* fix: `ruff` -> `ruff check` Original `ruff $@` is no longer supported by latest versions of ruff Signed-off-by: Jason C. Nucciarone <[email protected]> * fix!: add support for observing snap services Adds the `watch.yaml` file for configuring how the notices daemon observes services. The daemon will get the service alias from this file and use the alias to determine the proper hook to fire when the observed service is started or stopped. BREAKING CHANGES: __init__ for SystemdNotices now takes the Service data class instead of a generic list. The Service dataclass was added so that it would be easier to specify an alias for an observed service. Signed-off-by: Jason C. Nucciarone <[email protected]> * tests: update unit tests to reflect new notices API Signed-off-by: Jason C. Nucciarone <[email protected]> * tests: update integration tests * Consolidates metadata.yaml and actions.yaml into charmcraft.yaml for test charm. Less files to worry about. Signed-off-by: Jason C. Nucciarone <[email protected]> * docs: update lib documentation Signed-off-by: Jason C. Nucciarone <[email protected]> * chore(fmt): apply formatting rules Signed-off-by: Jason C. Nucciarone <[email protected]> * chore(lint): update copyright year Signed-off-by: Jason C. Nucciarone <[email protected]> * refactor: `open` -> `write_text` `yaml.dump()` returns a string if steam is none, so it is easier to just pass the content off to `write_text` instead of opening the file with a context manager. Signed-off-by: Jason C. Nucciarone <[email protected]> * fix(tests): correctly patch filesystem on python 3.8 Signed-off-by: Jason C. Nucciarone <[email protected]> * reactor: remove watch.yaml mechanism - Switch to passing the service names and aliases via argparse rather than using the pyyaml external dependency to create the watch.yaml file. - Use global map to track the observed service rather than caching the output of a watch.yaml read. Signed-off-by: Jason C. Nucciarone <[email protected]> * tests: update tests to not use watch.yaml - Reverted SystemdNotices in test charm back to the original constructor API. Signed-off-by: Jason C. Nucciarone <[email protected]> * fix(tests): remove pyfakefs as test dependency - Fixes unit tests failing on Python 3.10 due to incorrect patching. Signed-off-by: Jason C. Nucciarone <[email protected]> * refactor: remove explicit global references Signed-off-by: Jason C. Nucciarone <[email protected]> * docs: update example to use correct constructor arguments Signed-off-by: Jason C. Nucciarone <[email protected]> * chore: bump libpatch version Signed-off-by: Jason C. Nucciarone <[email protected]> --------- Signed-off-by: Jason C. Nucciarone <[email protected]>
canonical · Jul 21, 2024 · 9c7f617 · 9c7f617
1 parent 74ddb08
commit 9c7f617
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diff --git a/lib/charms/operator_libs_linux/v0/juju_systemd_notices.py b/lib/charms/operator_libs_linux/v0/juju_systemd_notices.py
@@ -1,5 +1,5 @@
 #!/usr/bin/python3
-# Copyright 2023 Canonical Ltd.
+# Copyright 2023-2024 Canonical Ltd.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -28,6 +28,7 @@
 
 ```python
 from charms.operator_libs_linux.v0.juju_systemd_notices import (
+    Service,
     ServiceStartedEvent,
     ServiceStoppedEvent,
     SystemdNotices,
@@ -41,7 +42,7 @@ def __init__(self, *args, **kwargs) -> None:
         super().__init__(*args, **kwargs)
 
         # Register services with charm. This adds the events to observe.
-        self._systemd_notices = SystemdNotices(self, ["slurmd"])
+        self._systemd_notices = SystemdNotices(self, [Service("snap.slurm.slurmd", alias="slurmd")])
         self.framework.observe(self.on.install, self._on_install)
         self.framework.observe(self.on.stop, self._on_stop)
         self.framework.observe(self.on.service_slurmd_started, self._on_slurmd_started)
@@ -58,7 +59,7 @@ def _on_install(self, _: InstallEvent) -> None:
     def _on_start(self, _: StartEvent) -> None:
         # This will trigger the juju-systemd-notices daemon to
         # emit a `service-slurmd-started` event.
-        systemd.service_start("slurmd")
+        snap.slurmd.enable()
 
     def _on_stop(self, _: StopEvent) -> None:
         # To stop the juju-systemd-notices service running in the background.
@@ -72,25 +73,25 @@ def _on_slurmd_started(self, _: ServiceStartedEvent) -> None:
 
         # This will trigger the juju-systemd-notices daemon to
         # emit a `service-slurmd-stopped` event.
-        systemd.service_stop("slurmd")
+        snap.slurmd.stop()
 
     def _on_slurmd_stopped(self, _: ServiceStoppedEvent) -> None:
         self.unit.status = BlockedStatus("slurmd not running")
 ```
 """
 
-__all__ = ["ServiceStartedEvent", "ServiceStoppedEvent", "SystemdNotices"]
+__all__ = ["Service", "ServiceStartedEvent", "ServiceStoppedEvent", "SystemdNotices"]
 
 import argparse
 import asyncio
 import functools
 import logging
-import re
 import signal
 import subprocess
 import textwrap
+from dataclasses import dataclass
 from pathlib import Path
-from typing import List
+from typing import List, Optional, Union
 
 from dbus_fast.aio import MessageBus
 from dbus_fast.constants import BusType, MessageType
@@ -107,16 +108,16 @@ def _on_slurmd_stopped(self, _: ServiceStoppedEvent) -> None:
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version.
-LIBPATCH = 1
+LIBPATCH = 2
 
 # juju-systemd-notices charm library dependencies.
 # Charm library dependencies are installed when the consuming charm is packed.
 PYDEPS = ["dbus-fast>=1.90.2"]
 
 _logger = logging.getLogger(__name__)
 _juju_unit = None
+_observed_services = {}
 _service_states = {}
-_service_hook_regex_filter = re.compile(r"service-(?P<service>[\w\\:-]*)-(?:started|stopped)")
 _DBUS_CHAR_MAPPINGS = {
     "_5f": "_",  # _ must be first since char mappings contain _.
     "_40": "@",
@@ -148,6 +149,19 @@ def _systemctl(*args) -> None:
 _disable_service = functools.partial(_systemctl, "disable")
 
 
+@dataclass
+class Service:
+    """Systemd service to observe.
+
+    Args:
+        name: Name of systemd service to observe on dbus.
+        alias: Event name alias for service.
+    """
+
+    name: str
+    alias: Optional[str] = None
+
+
 class ServiceStartedEvent(EventBase):
     """Event emitted when service has started."""
 
@@ -159,34 +173,52 @@ class ServiceStoppedEvent(EventBase):
 class SystemdNotices:
     """Observe systemd services on your machine base."""
 
-    def __init__(self, charm: CharmBase, services: List[str]) -> None:
+    def __init__(self, charm: CharmBase, services: List[Union[str, Service]]) -> None:
         """Instantiate systemd notices service."""
         self._charm = charm
-        self._services = services
+        self._services = [Service(s) if isinstance(s, str) else s for s in services]
         unit_name = self._charm.unit.name.replace("/", "-")
         self._service_file = Path(f"/etc/systemd/system/juju-{unit_name}-systemd-notices.service")
 
         _logger.debug(
             "Attaching systemd notice events to charm %s", self._charm.__class__.__name__
         )
-        for service in self._services:
-            self._charm.on.define_event(f"service_{service}_started", ServiceStartedEvent)
-            self._charm.on.define_event(f"service_{service}_stopped", ServiceStoppedEvent)
+        for s in self._services:
+            event = s.alias or s.name
+            self._charm.on.define_event(f"service_{event}_started", ServiceStartedEvent)
+            self._charm.on.define_event(f"service_{event}_stopped", ServiceStoppedEvent)
 
     def subscribe(self) -> None:
         """Subscribe charmed operator to observe status of systemd services."""
+        self._generate_hooks()
+        self._generate_service()
+        self._start()
+
+    def stop(self) -> None:
+        """Stop charmed operator from observing the status of subscribed services."""
+        _stop_service(self._service_file.name)
+        # Notices daemon is disabled so that the service will not restart after machine reboot.
+        _disable_service(self._service_file.name)
+
+    def _generate_hooks(self) -> None:
+        """Generate legacy event hooks for observed systemd services."""
         _logger.debug("Generating systemd notice hooks for %s", self._services)
-        start_hooks = [Path(f"hooks/service-{service}-started") for service in self._services]
-        stop_hooks = [Path(f"hooks/service-{service}-stopped") for service in self._services]
+        events = [s.alias or s.name for s in self._services]
+        start_hooks = [Path(f"hooks/service-{e}-started") for e in events]
+        stop_hooks = [Path(f"hooks/service-{e}-stopped") for e in events]
         for hook in start_hooks + stop_hooks:
             if hook.exists():
                 _logger.debug("Hook %s already exists. Skipping...", hook.name)
             else:
                 hook.symlink_to(self._charm.framework.charm_dir / "dispatch")
 
-        _logger.debug("Starting %s daemon", self._service_file.name)
+    def _generate_service(self) -> None:
+        """Generate systemd service file for notices daemon."""
+        _logger.debug("Generating service file %s", self._service_file.name)
         if self._service_file.exists():
             _logger.debug("Overwriting existing service file %s", self._service_file.name)
+
+        services = [f"{s.name}={s.alias or s.name}" for s in self._services]
         self._service_file.write_text(
             textwrap.dedent(
                 f"""
@@ -199,27 +231,31 @@ def subscribe(self) -> None:
                 Restart=always
                 WorkingDirectory={self._charm.framework.charm_dir}
                 Environment="PYTHONPATH={self._charm.framework.charm_dir / "venv"}"
-                ExecStart=/usr/bin/python3 {__file__} {self._charm.unit.name}
+                ExecStart=/usr/bin/python3 {__file__} --unit {self._charm.unit.name} {' '.join(services)}
 
                 [Install]
                 WantedBy=multi-user.target
                 """
             ).strip()
         )
-        _logger.debug("Service file %s written. Reloading systemd", self._service_file.name)
+
+        _logger.debug(
+            "Service file %s written. Reloading systemd manager configuration",
+            self._service_file.name,
+        )
+
+    def _start(self) -> None:
+        """Start systemd notices daemon to observe subscribed services."""
+        _logger.debug("Starting %s daemon", self._service_file.name)
+
+        # Reload systemd manager configuration so that it will pick up notices daemon.
         _daemon_reload()
-        # Notices daemon is enabled so that the service will start even after machine reboot.
-        # This functionality is needed in the event that a charm is rebooted to apply updates.
+
+        # Enable notices daemon to start after machine reboots.
         _enable_service(self._service_file.name)
         _start_service(self._service_file.name)
         _logger.debug("Started %s daemon", self._service_file.name)
 
-    def stop(self) -> None:
-        """Stop charmed operator from observing the status of subscribed services."""
-        _stop_service(self._service_file.name)
-        # Notices daemon is disabled so that the service will not restart after machine reboot.
-        _disable_service(self._service_file.name)
-
 
 def _name_to_dbus_path(name: str) -> str:
     """Convert the specified name into an org.freedesktop.systemd1.Unit path handle.
@@ -280,7 +316,6 @@ def _systemd_unit_changed(msg: Message) -> bool:
     if "ActiveState" not in properties:
         return False
 
-    global _service_states
     if service not in _service_states:
         _logger.debug("Dropping event for unwatched service: %s", service)
         return False
@@ -310,8 +345,9 @@ async def _send_juju_notification(service: str, state: str) -> None:
     if service.endswith(".service"):
         service = service[0:-len(".service")]  # fmt: skip
 
+    alias = _observed_services[service]
     event_name = "started" if state == "active" else "stopped"
-    hook = f"service-{service}-{event_name}"
+    hook = f"service-{alias}-{event_name}"
     cmd = ["/usr/bin/juju-exec", _juju_unit, f"hooks/{hook}"]
 
     _logger.debug("Invoking hook %s with command: %s", hook, " ".join(cmd))
@@ -363,30 +399,12 @@ async def _async_load_services() -> None:
     that should be watched. Upon finding a service hook it's current ActiveState
     will be queried from systemd to determine it's initial state.
     """
-    global _juju_unit
-    hooks_dir = Path.cwd() / "hooks"
-    _logger.info("Loading services from hooks in %s", hooks_dir)
-
-    if not hooks_dir.exists():
-        _logger.warning("Hooks dir %s does not exist.", hooks_dir)
-        return
-
-    watched_services = []
-    # Get service-{service}-(started|stopped) hooks defined by the charm.
-    for hook in hooks_dir.iterdir():
-        match = _service_hook_regex_filter.match(hook.name)
-        if match:
-            watched_services.append(match.group("service"))
-
-    _logger.info("Services from hooks are %s", watched_services)
-    if not watched_services:
-        return
-
     bus = await MessageBus(bus_type=BusType.SYSTEM).connect()
 
     # Loop through all the services and be sure that a new watcher is
     # started for new ones.
-    for service in watched_services:
+    _logger.info("Services to observe are %s", _observed_services)
+    for service in _observed_services:
         # The .service suffix is necessary and will cause lookup failures of the
         # service unit when readying the watcher if absent from the service name.
         service = f"{service}.service"
@@ -462,13 +480,18 @@ def _main():
     """
     parser = argparse.ArgumentParser()
     parser.add_argument("-d", "--debug", action="store_true")
-    parser.add_argument("unit", type=str)
+    parser.add_argument("--unit", type=str)
+    parser.add_argument("services", nargs="*")
     args = parser.parse_args()
 
     # Intentionally set as global.
     global _juju_unit
     _juju_unit = args.unit
 
+    for s in args.services:
+        service, alias = s.split("=")
+        _observed_services[service] = alias
+
     console_handler = logging.StreamHandler()
     if args.debug:
         _logger.setLevel(logging.DEBUG)

diff --git a/tests/integration/juju_systemd_notices/notices-charm/actions.yaml b/tests/integration/juju_systemd_notices/notices-charm/actions.yaml
diff --git a/tests/integration/juju_systemd_notices/notices-charm/charmcraft.yaml b/tests/integration/juju_systemd_notices/notices-charm/charmcraft.yaml
@@ -1,6 +1,12 @@
-# Copyright 2023 Canonical Ltd.
+# Copyright 2023-2024 Canonical Ltd.
 # See LICENSE file for licensing details.
 
+name: juju-systemd-notices
+description: |
+  Test charm used for the juju_systemd_notices charm library integration tests.
+summary: |
+  A charm with a minimal daemon for testing the juju-systemd-notices charm library.
+
 type: charm
 bases:
   - build-on:
@@ -9,3 +15,8 @@ bases:
     run-on:
     - name: ubuntu
       channel: "22.04"
+
+actions:
+  stop-service:
+    description: Stop internal test service inside charm
+
diff --git a/tests/integration/juju_systemd_notices/notices-charm/metadata.yaml b/tests/integration/juju_systemd_notices/notices-charm/metadata.yaml
diff --git a/tests/integration/juju_systemd_notices/notices-charm/src/charm.py b/tests/integration/juju_systemd_notices/notices-charm/src/charm.py
@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# Copyright 2023 Canonical Ltd.
+# Copyright 2023-2024 Canonical Ltd.
 # See LICENSE file for licensing details.
 
 """Minimal charm for testing the juju_systemd_notices charm library.