feat: Log addition of config watchers and make receivers unique (#487)

- Add log message for each model the ConfigWatcher is listening to, mostly
  so I can tell whether this app is even getting loaded.
- Add dispatch_uid to receivers so that if `ready` (or `connect_receivers`)
  is called more than once, the receiver is only attached once. (This is
  not a response to an observed problem -- it's just a best practice
  according to Django docs.)

CHANGELOG.rst

@@ -14,6 +14,15 @@ Change Log
 Unreleased
 ~~~~~~~~~~
 
+[3.1.0] - 2023-10-31
+~~~~~~~~~~~~~~~~~~~~
+
+Changed
+_______
+
+* Add log message for each model the ConfigWatcher is listening to
+* Ensure that ConfigWatcher only attaches receivers once
+
 [3.0.0] - 2023-10-30
 ~~~~~~~~~~~~~~~~~~~~
 

edx_arch_experiments/__init__.py

@@ -2,4 +2,4 @@
 A plugin to include applications under development by the architecture team at 2U.
 """
 
-__version__ = '3.0.0'
+__version__ = '3.1.0'

edx_arch_experiments/config_watcher/signals/receivers.py

@@ -99,21 +99,23 @@ def _register_waffle_observation(*, model, short_name, fields):
         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)
+    @receiver(signals.post_save, sender=model, dispatch_uid=f"config_watcher_{short_name}_change")
     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)
+    @receiver(signals.post_delete, sender=model, dispatch_uid=f"config_watcher_{short_name}_delete")
     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}")
 
+    log.info(f"Watching {model.__module__}.{model.__qualname__} for changes")
+
 
 def connect_receivers():
     """