Allow ReplicationRestResource to be added to workers (#7515)

This allows workers to talk to each other over HTTP replication.

changelog.d/7515.misc

@@ -0,0 +1 @@
+Allow `ReplicationRestResource` to be added to workers.

synapse/app/generic_worker.py

@@ -47,6 +47,7 @@ from synapse.http.site import SynapseSite
 from synapse.logging.context import LoggingContext
 from synapse.metrics import METRICS_PREFIX, MetricsResource, RegistryProxy
 from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.replication.http import REPLICATION_PREFIX, ReplicationRestResource
 from synapse.replication.slave.storage._base import BaseSlavedStore
 from synapse.replication.slave.storage.account_data import SlavedAccountDataStore
 from synapse.replication.slave.storage.appservice import SlavedApplicationServiceStore
@@ -570,6 +571,9 @@ class GenericWorkerServer(HomeServer):
                 if name in ["keys", "federation"]:
                     resources[SERVER_KEY_V2_PREFIX] = KeyApiV2Resource(self)
 
+                if name == "replication":
+                    resources[REPLICATION_PREFIX] = ReplicationRestResource(self)
+
         root_resource = create_resource_tree(resources, NoResource())
 
         _base.listen_tcp(

synapse/replication/http/__init__.py

@@ -34,8 +34,11 @@ class ReplicationRestResource(JsonResource):
 
     def register_servlets(self, hs):
         send_event.register_servlets(hs, self)
-        membership.register_servlets(hs, self)
         federation.register_servlets(hs, self)
+
+        # The following can't currently be instantiated on workers.
+        if hs.config.worker.worker_app is None:
+            membership.register_servlets(hs, self)
             login.register_servlets(hs, self)
             register.register_servlets(hs, self)
             devices.register_servlets(hs, self)