Add config option to disable media_repo on main synapse

... to stop us doing the cache cleanup jobs on the master.

docs/workers.rst

@@ -170,6 +170,10 @@ Handles the media repository. It can handle all endpoints starting with::
 
     /_matrix/media/
 
+You should also set ``enable_media_repo: False`` in the shared configuration
+file to stop the main synapse running background jobs related to managing the
+media repository.
+
 Note this worker cannot be load-balanced: only one instance should be active.
 
 ``synapse.app.client_reader``
@@ -203,4 +207,3 @@ the ``worker_main_http_uri`` setting in the frontend_proxy worker configuration
 file. For example::
 
     worker_main_http_uri: http://127.0.0.1:8008
-

synapse/app/homeserver.py

@@ -194,6 +194,7 @@ class SynapseHomeServer(HomeServer):
             })
 
         if name in ["media", "federation", "client"]:
+            if self.get_config().enable_media_repo:
                 media_repo = self.get_media_repository_resource()
                 resources.update({
                     MEDIA_PREFIX: media_repo,
@@ -202,6 +203,10 @@ class SynapseHomeServer(HomeServer):
                         self, self.config.uploads_path
                     ),
                 })
+            elif name == "media":
+                raise ConfigError(
+                    "'media' resource conflicts with enable_media_repo=False",
+                )
 
         if name in ["keys", "federation"]:
             resources.update({

synapse/app/media_repository.py

@@ -150,6 +150,13 @@ def start(config_options):
 
     assert config.worker_app == "synapse.app.media_repository"
 
+    if config.enable_media_repo:
+        _base.quit_with_error(
+            "enable_media_repo must be disabled in the main synapse process\n"
+            "before the media repo can be run in a separate worker.\n"
+            "Please add ``enable_media_repo: false`` to the main config\n"
+        )
+
     setup_logging(config, use_worker_options=True)
 
     events.USE_FROZEN_DICTS = config.use_frozen_dicts

synapse/config/server.py

@@ -41,6 +41,12 @@ class ServerConfig(Config):
         # false only if we are updating the user directory in a worker
         self.update_user_directory = config.get("update_user_directory", True)
 
+        # whether to enable the media repository endpoints. This should be set
+        # to false if the media repository is running as a separate endpoint;
+        # doing so ensures that we will not run cache cleanup jobs on the
+        # master, potentially causing inconsistency.
+        self.enable_media_repo = config.get("enable_media_repo", True)
+
         self.filter_timeline_limit = config.get("filter_timeline_limit", -1)
 
         # Whether we should block invites sent to users on this server