1 files changed, 39 insertions, 1 deletions
diff --git a/synapse/config/workers.py b/synapse/config/workers.py
index 38e13dd7b5..0b9789160c 100644
--- a/synapse/config/workers.py
+++ b/synapse/config/workers.py
@@ -15,7 +15,7 @@
 
 import argparse
 import logging
-from typing import Any, Dict, List, Union
+from typing import Any, Dict, List, Optional, Union
 
 import attr
 from pydantic import BaseModel, Extra, StrictBool, StrictInt, StrictStr
@@ -148,6 +148,27 @@ class WriterLocations:
     )
 
 
+@attr.s(auto_attribs=True)
+class OutboundFederationRestrictedTo:
+    """Whether we limit outbound federation to a certain set of instances.
+
+    Attributes:
+        instances: optional list of instances that can make outbound federation
+            requests. If None then all instances can make federation requests.
+        locations: list of instance locations to connect to proxy via.
+    """
+
+    instances: Optional[List[str]]
+    locations: List[InstanceLocationConfig] = attr.Factory(list)
+
+    def __contains__(self, instance: str) -> bool:
+        # It feels a bit dirty to return `True` if `instances` is `None`, but it makes
+        # sense in downstream usage in the sense that if
+        # `outbound_federation_restricted_to` is not configured, then any instance can
+        # talk to federation (no restrictions so always return `True`).
+        return self.instances is None or instance in self.instances
+
+
 class WorkerConfig(Config):
     """The workers are processes run separately to the main synapse process.
     They have their own pid_file and listener configuration. They use the
@@ -357,6 +378,23 @@ class WorkerConfig(Config):
             new_option_name="update_user_directory_from_worker",
         )
 
+        outbound_federation_restricted_to = config.get(
+            "outbound_federation_restricted_to", None
+        )
+        self.outbound_federation_restricted_to = OutboundFederationRestrictedTo(
+            outbound_federation_restricted_to
+        )
+        if outbound_federation_restricted_to:
+            for instance in outbound_federation_restricted_to:
+                if instance not in self.instance_map:
+                    raise ConfigError(
+                        "Instance %r is configured in 'outbound_federation_restricted_to' but does not appear in `instance_map` config."
+                        % (instance,)
+                    )
+                self.outbound_federation_restricted_to.locations.append(
+                    self.instance_map[instance]
+                )
+
     def _should_this_worker_perform_duty(
         self,
         config: Dict[str, Any],