feat: Add Waffle config watcher (#481)

Listens to Waffle model changes and reports them 1) to the log and 2) to
a Slack webhook.

This adds a dependency on django-waffle.

CHANGELOG.rst

@@ -13,6 +13,14 @@ Change Log
 
 Unreleased
 ~~~~~~~~~~
+
+[2.2.0] - 2023-10-27
+~~~~~~~~~~~~~~~~~~~~
+
+Added
+_____
+
+* Add ``edx_arch_experiments.config_watcher`` Django app for monitoring Waffle changes
 * Add script to get github action errors
 * Add script to republish failed events
 

edx_arch_experiments/__init__.py

@@ -2,4 +2,4 @@
 A plugin to include applications under development by the architecture team at 2U.
 """
 
-__version__ = '2.1.0'
+__version__ = '2.2.0'

edx_arch_experiments/config_watcher/apps.py

@@ -0,0 +1,17 @@
+"""
+App for reporting configuration changes to Slack for operational awareness.
+"""
+
+from django.apps import AppConfig
+
+
+class ConfigWatcherApp(AppConfig):
+    """
+    Django application to report configuration changes to operators.
+    """
+    name = 'edx_arch_experiments.config_watcher'
+
+    def ready(self):
+        from .signals import receivers  # pylint: disable=import-outside-toplevel
+
+        receivers.connect_receivers()

edx_arch_experiments/config_watcher/signals/receivers.py

@@ -0,0 +1,123 @@
+"""
+Signal receivers for the config watcher.
+
+Call ``connect_receivers`` to initialize.
+"""
+
+import html
+import json
+import logging
+import urllib.request
+
+import waffle.models
+from django.conf import settings
+from django.db.models import signals
+from django.dispatch import receiver
+
+log = logging.getLogger(__name__)
+
+# .. setting_name: CONFIG_WATCHER_SLACK_WEBHOOK_URL
+# .. setting_default: None
+# .. setting_description: Slack webhook URL to send config change events to.
+#   If not configured, this functionality is disabled.
+CONFIG_WATCHER_SLACK_WEBHOOK_URL = getattr(settings, 'CONFIG_WATCHER_SLACK_WEBHOOK_URL', None)
+
+
+def _send_to_slack(message):
+    """Send this message as plain text to the configured Slack channel."""
+    if not CONFIG_WATCHER_SLACK_WEBHOOK_URL:
+        return
+
+    # https://api.slack.com/reference/surfaces/formatting
+    body_data = {
+        'text': html.escape(message, quote=False)
+    }
+
+    req = urllib.request.Request(
+        url=CONFIG_WATCHER_SLACK_WEBHOOK_URL, data=json.dumps(body_data).encode(),
+        headers={"Content-Type": "application/json"},
+    )
+    with urllib.request.urlopen(req, timeout=2) as resp:
+        status = resp.getcode()
+        if status != 200:
+            log.error(f"Slack rejected the config watcher message. {status=}, body={resp.read().decode('utf-8')}")
+
+
+def _report_config_change(message):
+    """
+    Report this message string as a configuration change.
+
+    Sends to logs and to Slack.
+    """
+    log.info(message)
+    _send_to_slack(message)
+
+
+def _report_waffle_change(model_short_name, instance, created, fields):
+    """
+    Report that a model instance has been created or updated.
+    """
+    verb = "created" if created else "updated"
+    state_desc = ", ".join(f"{field}={repr(getattr(instance, field))}" for field in fields)
+    _report_config_change(f"Waffle {model_short_name} {instance.name!r} was {verb}. New config: {state_desc}")
+
+
+def _report_waffle_delete(model_short_name, instance):
+    """
+    Report that a model instance has been deleted.
+    """
+    _report_config_change(f"Waffle {model_short_name} {instance.name!r} was deleted")
+
+
+# List of models to observe. Each is a dictionary that matches the
+# keyword args of _register_waffle_observation.
+_WAFFLE_MODELS_TO_OBSERVE = [
+    {
+        'model': waffle.models.Flag,
+        'short_name': 'flag',
+        'fields': ['everyone', 'percent', 'superusers', 'staff', 'authenticated', 'note', 'languages'],
+    },
+    {
+        'model': waffle.models.Switch,
+        'short_name': 'switch',
+        'fields': ['active', 'note'],
+    },
+    {
+        'model': waffle.models.Sample,
+        'short_name': 'sample',
+        'fields': ['percent', 'note'],
+    },
+]
+
+
+def _register_waffle_observation(*, model, short_name, fields):
+    """
+    Register a Waffle model for observation according to config values.
+
+    Args:
+        model (class): The model class to monitor
+        short_name (str): A short descriptive name for an instance of the model, e.g. "flag"
+        fields (list): Names of fields to report on in the Slack message
+    """
+    @receiver(signals.post_save, sender=model)
+    def report_waffle_change(*args, instance, created, **kwargs):
+        try:
+            _report_waffle_change(short_name, instance, created, fields)
+        except:  # noqa pylint: disable=bare-except
+            # Log and suppress error so Waffle change can proceed
+            log.exception(f"Failed to report change to waffle {short_name}")
+
+    @receiver(signals.post_delete, sender=model)
+    def report_waffle_delete(*args, instance, **kwargs):
+        try:
+            _report_waffle_delete(short_name, instance)
+        except:  # noqa pylint: disable=bare-except
+            log.exception(f"Failed to report deletion of waffle {short_name}")
+
+
+def connect_receivers():
+    """
+    Initialize application's receivers.
+    """
+    for config in _WAFFLE_MODELS_TO_OBSERVE:
+        _register_waffle_observation(**config)

requirements/base.in

@@ -3,3 +3,4 @@
 
 Django             # Web application framework
 edx_django_utils
+django-waffle            # Configuration switches and flags -- used by config_watcher app

requirements/base.txt

@@ -20,7 +20,9 @@ django==3.2.22
 django-crum==0.7.9
     # via edx-django-utils
 django-waffle==4.0.0
-    # via edx-django-utils
+    # via
+    #   -r requirements/base.in
+    #   edx-django-utils
 edx-django-utils==5.7.0
     # via -r requirements/base.in
 newrelic==9.1.0