Retain state (#66)

* persist state on graceful shutdown

* unit test

* dependencies already specified in pyproject.yaml

* changelog entry

* bump version

* add no cover

* Update cos_alerter/alerter.py

Co-authored-by: PietroPasotti <pietro.pasotti@canonical.com>

* more appropriate variable name

* bump version in changelog

---------

Co-authored-by: PietroPasotti <pietro.pasotti@canonical.com>

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.7.0] - 2024-02-26
+
+- Client state is now retained on a graceful shutdown (#66).
+
 ## [0.6.0] - 2023-11-30
 
 - Added badges to README.md (#62).

README.md

@@ -9,7 +9,7 @@ COS Alerter is intended to be used together with alertmanager and prometheus:
 - Liveness of COS Alerter itself from a metric endpoint it exposes and prometheus scrapes
 ## Configuring Alertmanager
 
-In order to integrate with COS Alerter you need to a heartbeat rule to Prometheus and Add a route to the Alertmanager config
+In order to integrate with COS Alerter you need to add a heartbeat rule to Prometheus and add a route to the Alertmanager config.
 
 If you are using the Canonical Observability Stack, the alert rule is already created for you. If not, you can use a rule similar to the following:
 ```yaml

cos_alerter/alerter.py

@@ -4,6 +4,7 @@
 """Main logic for COS Alerter."""
 
 import datetime
+import json
 import logging
 import os
 import sys
@@ -15,6 +16,7 @@
 
 import apprise
 import durationpy
+import xdg_base_dirs
 from ruamel.yaml import YAML
 from ruamel.yaml.constructor import DuplicateKeyError
 
@@ -69,6 +71,13 @@ def reload(self):
             self.data["notify"]["repeat_interval"]
         ).total_seconds()
 
+        # Static variables. We define them here so it is easy to expose them later as config
+        # values if needed.
+        base_dir = xdg_base_dirs.xdg_state_home() / "cos_alerter"
+        if not base_dir.exists():
+            base_dir.mkdir(parents=True)
+        self.data["clients_file"] = base_dir / "clients.state"
+
 
 def deep_update(base: dict, new: typing.Optional[dict]):
     """Deep dict update.
@@ -151,6 +160,42 @@ def initialize():
                 "notify_time": None,
             }
 
+        # Recover any state that was dumped on last exit.
+        if config["clients_file"].exists():
+            with config["clients_file"].open() as f:
+                existing_clients = json.load(f)
+            config["clients_file"].unlink()
+            for client in existing_clients:
+                if client in state["clients"]:
+                    state["clients"][client]["alert_time"] = existing_clients[client]["alert_time"]
+                    state["clients"][client]["notify_time"] = existing_clients[client][
+                        "notify_time"
+                    ]
+
+    # This is difficult to test in unit tests because it acquires and does not release all of the
+    # locks. When integration tests have been solved we need to remove the "no cover" from this
+    # method.
+    @staticmethod
+    def dump_and_pause():  # pragma: no cover
+        """Dump the state of the program and exit gracefully.
+
+        This function acquires all the locks and never releases them, effectively pausing the
+        program.
+        """
+        logger.info("Starting safe shutdown.")
+        for client in state["clients"]:
+            state["clients"][client]["lock"].acquire()
+        # Locks are not json serializable.
+        clients_without_locks = {
+            client: {
+                "alert_time": state["clients"][client]["alert_time"],
+                "notify_time": state["clients"][client]["notify_time"],
+            }
+            for client in state["clients"]
+        }
+        with config["clients_file"].open("w") as f:
+            json.dump(clients_without_locks, f)
+
     @staticmethod
     def clients():
         """Return a list of clientids."""
@@ -170,7 +215,12 @@ def is_down(self) -> bool:
         """Determine if Alertmanager should be considered down based on the last alert."""
         if self.data["alert_time"] is None:
             return False
-        return time.monotonic() - self.data["alert_time"] > config["watch"]["down_interval"]
+        # We need to take the max of the alert and the start time, so that we only count time when
+        # cos-alerter was running.
+        return (
+            time.monotonic() - max(self.data["alert_time"], self.start_time)
+            > config["watch"]["down_interval"]
+        )
 
     def _recently_notified(self) -> bool:
         """Determine if a notification has been previously sent within the repeat interval."""

cos_alerter/daemon.py

@@ -28,6 +28,13 @@ def sigint(_, __):  # pragma: no cover
     sys.exit()
 
 
+def sigterm(_, __):  # pragma: no cover
+    """Signal handler for graceful shutdown on sigterm."""
+    logger.info("Shutting down.")
+    AlerterState.dump_and_pause()
+    sys.exit()
+
+
 def sigusr1(_, __):  # pragma: no cover
     """Signal handler for SIGUSR1 which sends a test notification."""
     logger.info("Received SIGUSR1.")
@@ -82,6 +89,7 @@ def main(run_for: Optional[int] = None, argv: List[str] = sys.argv):
     # Observe signal handlers
     try:  # pragma: no cover
         signal.signal(signal.SIGINT, sigint)
+        signal.signal(signal.SIGTERM, sigterm)
         signal.signal(signal.SIGUSR1, sigusr1)
         logger.debug("Signal handlers set.")
     except ValueError as e:

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "cos-alerter"
-version = "0.6.0"
+version = "0.7.0"
 authors = [
   { name="Dylan Stephano-Shachter", email="dylan.stephano-shachter@canonical.com" }
 ]
@@ -24,9 +24,10 @@ dependencies = [
   "flask~=2.2",
   "prometheus_flask_exporter~=0.22",
   "pyyaml~=6.0",
+  "ruamel.yaml~=0.18.0",
   "timeago~=1.0",
   "waitress~=2.1",
-  "ruamel.yaml~=0.18.0"
+  "xdg-base-dirs~=6.0.1",
 ]
 
 [project.urls]
@@ -45,14 +46,16 @@ line-length = 99
 [tool.ruff]
 line-length = 99
 extend-exclude = ["__pycache__", "*.egg_info"]
+
+[tool.ruff.lint]
 select = ["E", "W", "F", "C", "N", "R", "D", "I001"]
 # Ignore E501 because using black creates errors with this
 # Ignore D107 Missing docstring in __init__
 ignore = ["E501", "D107"]
 # D100, D101, D102, D103: Ignore missing docstrings in tests
 per-file-ignores = {"tests/*" = ["D100","D101","D102","D103"]}
 
-[tool.ruff.pydocstyle]
+[tool.ruff.lint.pydocstyle]
 convention = "google"
 
 [tool.pyright]

rockcraft.yaml

@@ -1,7 +1,7 @@
 name: cos-alerter
 summary: A liveness checker for self-monitoring.
 description: Receive regular pings from the cos stack and alert when they stop.
-version: "0.6.0"  # NOTE: Make sure this matches `cos-alerter` below
+version: "0.7.0"  # NOTE: Make sure this matches `cos-alerter` below
 base: ubuntu:22.04
 license: Apache-2.0
 platforms:
@@ -11,7 +11,7 @@ parts:
     plugin: python
     source: .
     python-packages:
-      - cos-alerter==0.6.0  # NOTE: Make sure this matches `version` above
+      - cos-alerter==0.7.0  # NOTE: Make sure this matches `version` above
     stage-packages:
       - python3-venv
 services:

snap/snapcraft.yaml

@@ -1,5 +1,5 @@
 name: cos-alerter
-version: '0.6.0'
+version: '0.7.0'
 summary: A watchdog alerting on alertmanager notification failures.
 license: Apache-2.0
 contact: simon.aronsson@canonical.com

tests/test_alerter.py

@@ -164,6 +164,30 @@ def test_is_down_with_wait_for_first_connection(monotonic_mock, fake_fs):
         assert state.is_down() is True  # 5.5 minutes since reset_alert_timeout() was called.
 
 
+@freezegun.freeze_time("2023-01-01")
+@unittest.mock.patch("time.monotonic")
+def test_is_down_from_graceful_shutdown(monotonic_mock, fake_fs):
+    with open("/etc/cos-alerter.yaml") as f:
+        conf = yaml.safe_load(f)
+    conf["watch"]["wait_for_first_connection"] = True
+    with open("/etc/cos-alerter.yaml", "w") as f:
+        yaml.dump(conf, f)
+    config.reload()
+    fake_fs.create_file(config["clients_file"])
+    with config["clients_file"].open("w") as f:
+        f.write('{"clientid1": {"alert_time": 500, "notify_time": null}}')
+    monotonic_mock.return_value = 1000
+    print("Hello Test")
+    AlerterState.initialize()
+    state = AlerterState(clientid="clientid1")
+    with state:
+        print(list(AlerterState.clients()))
+        print(state.data)
+        assert state.is_down() is False
+        monotonic_mock.return_value = 2330
+        assert state.is_down() is True
+
+
 @freezegun.freeze_time("2023-01-01")
 @unittest.mock.patch("time.monotonic")
 def test_is_down(monotonic_mock, fake_fs):

tox.ini

@@ -45,9 +45,7 @@ deps =
     freezegun
     pyfakefs
     pytest
-    pyyaml
     werkzeug
-    ruamel.yaml
 commands =
     coverage run --source {[vars]src_path} -m pytest -m "not slow" -v --log-cli-level=INFO {[vars]tst_path}
 
@@ -59,8 +57,6 @@ deps =
     freezegun
     pyfakefs
     pytest
-    pyyaml
-    ruamel.yaml
 commands =
     coverage run -a --source {[vars]src_path} -m pytest -m slow -v --log-cli-level=INFO {[vars]tst_path}