fix: ConfigWatcher needs to register receivers using strong references

These inner functions would otherwise get GC'd right away, since Django
only holds weak references to receivers by default. (I don't know why this
worked in devstack.)

CHANGELOG.rst

@@ -14,6 +14,12 @@ Change Log
 Unreleased
 ~~~~~~~~~~
 
+[3.1.1] - 2023-11-06
+~~~~~~~~~~~~~~~~~~~~
+Fixed
+_____
+* ConfigWatcher should now respond to model events properly now that it registers receivers with strong references. (Tested in sandbox.)
+
 [3.1.0] - 2023-10-31
 ~~~~~~~~~~~~~~~~~~~~
 

edx_arch_experiments/__init__.py

@@ -2,4 +2,4 @@
 A plugin to include applications under development by the architecture team at 2U.
 """
 
-__version__ = '3.1.0'
+__version__ = '3.1.1'

edx_arch_experiments/config_watcher/signals/receivers.py

@@ -99,15 +99,22 @@ 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, dispatch_uid=f"config_watcher_{short_name}_change")
+
+    # Note that weak=False is required here. Django by default only
+    # holds weak references to receiver functions. But these inner
+    # functions would then be garbage-collected, and Django would drop
+    # them. So pass weak=False to make Django hold strong references
+    # instead. (For some reason, this isn't needed in devstack...)
+
+    @receiver(signals.post_save, sender=model, weak=False, 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, dispatch_uid=f"config_watcher_{short_name}_delete")
+    @receiver(signals.post_delete, sender=model, weak=False, dispatch_uid=f"config_watcher_{short_name}_delete")
     def report_waffle_delete(*args, instance, **kwargs):
         try:
             _report_waffle_delete(short_name, instance)