Only enable this functionality for Redis-based deployments

TCP replication's 'direct to master' style does not interact well, and besides,

TCP replication is obsolete.

changelog.d/12251.feature

@@ -1 +1 @@
-Move `update_client_ip` background job from the main process to the background worker.
+Offload the `update_client_ip` background job from the main process to the background worker, when using Redis-based replication.

synapse/storage/databases/main/client_ips.py

@@ -408,7 +408,13 @@ def __init__(
     ):
         super().__init__(database, db_conn, hs)
 
-        self._update_on_this_worker = hs.config.worker.run_background_tasks
+        if hs.config.redis.redis_enabled:
+            # If we're using Redis, we can shift this update process off to
+            # the background worker
+            self._update_on_this_worker = hs.config.worker.run_background_tasks
+        else:
+            # If we're NOT using Redis, this must be handled by the master
+            self._update_on_this_worker = hs.get_instance_name() == "master"
 
         self.user_ips_max_age = hs.config.server.user_ips_max_age
 

synapse/storage/databases/main/monthly_active_users.py

@@ -46,7 +46,13 @@ def __init__(
         self._clock = hs.get_clock()
         self.hs = hs
 
-        self._update_on_this_worker = hs.config.worker.run_background_tasks
+        if hs.config.redis.redis_enabled:
+            # If we're using Redis, we can shift this update process off to
+            # the background worker
+            self._update_on_this_worker = hs.config.worker.run_background_tasks
+        else:
+            # If we're NOT using Redis, this must be handled by the master
+            self._update_on_this_worker = hs.get_instance_name() == "master"
 
         self._limit_usage_by_mau = hs.config.server.limit_usage_by_mau
         self._max_mau_value = hs.config.server.max_mau_value