Disable IP storage via environment variable

Env var because it avoids fiddling with a tonne of tests.

synapse/storage/databases/main/client_ips.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import logging
+from os import environ
 from typing import TYPE_CHECKING, Dict, List, Mapping, Optional, Tuple, Union, cast
 
 import attr
@@ -42,6 +43,8 @@
 # 120 seconds == 2 minutes
 LAST_SEEN_GRANULARITY = 120 * 1000
 
+DISABLE_CLIENT_IP_STORAGE = environ.get("SYNAPSE_DISABLE_CLIENT_IP_STORAGE") == "true"
+
 
 @attr.s(slots=True, frozen=True, auto_attribs=True)
 class DeviceLastConnectionInfo:
@@ -586,6 +589,10 @@ async def insert_client_ip(
         device_id: Optional[str],
         now: Optional[int] = None,
     ) -> None:
+        # Beep: don't bother storing client IPs at all (if env set)
+        if DISABLE_CLIENT_IP_STORAGE:
+            return
+
         # The sync proxy continuously triggers /sync even if the user is not
         # present so should be excluded from user_ips entries.
         if user_agent == "sync-v3-proxy-":