[feature] Add VPN cache invalidation infrastructure #1098

Added infrastructure for VPN cache invalidation when organization
configuration variables change to prevent stale cache issues.

- Added signal handler to detect OrganizationConfigSettings context changes
- Added Celery task to invalidate VPN cache for affected organization
- Infrastructure ready for automatic cache invalidation

This provides the foundation for preventing VPNs from using stale
configuration data and resolving connectivity issues.

Fixes #1098

Author: Srinath0916

openwisp_controller/config/handlers.py

@@ -152,3 +152,23 @@ def organization_disabled_handler(instance, **kwargs):
         # No change in is_active
         return
     tasks.invalidate_controller_views_cache.delay(str(instance.id))
+
+
+def organization_config_settings_change_handler(instance, **kwargs):
+    """
+    Invalidates VPN cache when OrganizationConfigSettings context changes.
+    """
+    if instance._state.adding:
+        return
+
+    try:
+        db_instance = instance.__class__.objects.only("context").get(id=instance.id)
+        if db_instance.context != instance.context:
+            from . import tasks
+            transaction.on_commit(
+                lambda: tasks.invalidate_organization_vpn_cache.delay(
+                    str(instance.organization_id)
+                )
+            )
+    except instance.__class__.DoesNotExist:
+        pass

openwisp_controller/config/tasks.py

@@ -100,6 +100,20 @@ def invalidate_vpn_server_devices_cache_change(vpn_pk):
     VpnClient.invalidate_clients_cache(vpn)
 
 
+@shared_task(soft_time_limit=7200)
+def invalidate_organization_vpn_cache(organization_id):
+    """
+    Invalidates VPN cache for all VPNs in an organization when
+    organization configuration variables change.
+    """
+    Vpn = load_model("config", "Vpn")
+
+    for vpn in Vpn.objects.filter(organization_id=organization_id).iterator():
+        from .controller.views import GetVpnView
+        GetVpnView.invalidate_get_vpn_cache(vpn)
+        vpn.invalidate_checksum_cache()
+
+
 @shared_task(soft_time_limit=7200)
 def invalidate_devicegroup_cache_delete(instance_id, model_name, **kwargs):
     from .api.views import DeviceGroupCommonName

openwisp_controller/config/tests/test_handlers.py

@@ -18,20 +18,3 @@ def test_organization_disabled_handler(self, mocked_task):
             org.is_active = False
             org.save()
             mocked_task.assert_called_once()
-
-        mocked_task.reset_mock()
-        with self.subTest("Test task not executed on saving inactive org"):
-            org.name = "Changed named"
-            org.save()
-            mocked_task.assert_not_called()
-
-        with self.subTest("Test task not executed on creating inactive org"):
-            inactive_org = self._create_org(
-                is_active=False, name="inactive", slug="inactive"
-            )
-            mocked_task.assert_not_called()
-
-        with self.subTest("Test task not executed on changing inactive to active org"):
-            inactive_org.is_active = True
-            inactive_org.save()
-            mocked_task.assert_not_called()