4 files changed, 44 insertions, 0 deletions
diff --git a/synapse/replication/tcp/client.py b/synapse/replication/tcp/client.py
index 52a0aefe68..fc06a7b053 100644
--- a/synapse/replication/tcp/client.py
+++ b/synapse/replication/tcp/client.py
@@ -143,6 +143,9 @@ class ReplicationClientHandler(AbstractReplicationClientHandler):
         if d:
             d.callback(data)
 
+    def on_remote_server_up(self, server: str):
+        """Called when get a new REMOTE_SERVER_UP command."""
+
     def get_streams_to_replicate(self) -> Dict[str, int]:
         """Called when a new connection has been established and we need to
         subscribe to streams.
diff --git a/synapse/replication/tcp/commands.py b/synapse/replication/tcp/commands.py
index cbb36b9acf..451671412d 100644
--- a/synapse/replication/tcp/commands.py
+++ b/synapse/replication/tcp/commands.py
@@ -387,6 +387,20 @@ class UserIpCommand(Command):
         )
 
 
+class RemoteServerUpCommand(Command):
+    """Sent when a worker has detected that a remote server is no longer
+    "down" and retry timings should be reset.
+
+    If sent from a client the server will relay to all other workers.
+
+    Format::
+
+        REMOTE_SERVER_UP <server>
+    """
+
+    NAME = "REMOTE_SERVER_UP"
+
+
 _COMMANDS = (
     ServerCommand,
     RdataCommand,
@@ -401,6 +415,7 @@ _COMMANDS = (
     RemovePusherCommand,
     InvalidateCacheCommand,
     UserIpCommand,
+    RemoteServerUpCommand,
 )  # type: Tuple[Type[Command], ...]
 
 # Map of command name to command type.
@@ -414,6 +429,7 @@ VALID_SERVER_COMMANDS = (
     ErrorCommand.NAME,
     PingCommand.NAME,
     SyncCommand.NAME,
+    RemoteServerUpCommand.NAME,
 )
 
 # The commands the client is allowed to send
@@ -427,4 +443,5 @@ VALID_CLIENT_COMMANDS = (
     InvalidateCacheCommand.NAME,
     UserIpCommand.NAME,
     ErrorCommand.NAME,
+    RemoteServerUpCommand.NAME,
 )
diff --git a/synapse/replication/tcp/protocol.py b/synapse/replication/tcp/protocol.py
index 5f4bdf84d2..131e5acb09 100644
--- a/synapse/replication/tcp/protocol.py
+++ b/synapse/replication/tcp/protocol.py
@@ -76,6 +76,7 @@ from synapse.replication.tcp.commands import (
     PingCommand,
     PositionCommand,
     RdataCommand,
+    RemoteServerUpCommand,
     ReplicateCommand,
     ServerCommand,
     SyncCommand,
@@ -460,6 +461,9 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
     async def on_INVALIDATE_CACHE(self, cmd):
         self.streamer.on_invalidate_cache(cmd.cache_func, cmd.keys)
 
+    async def on_REMOTE_SERVER_UP(self, cmd: RemoteServerUpCommand):
+        self.streamer.on_remote_server_up(cmd.data)
+
     async def on_USER_IP(self, cmd):
         self.streamer.on_user_ip(
             cmd.user_id,
@@ -555,6 +559,9 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
     def send_sync(self, data):
         self.send_command(SyncCommand(data))
 
+    def send_remote_server_up(self, server: str):
+        self.send_command(RemoteServerUpCommand(server))
+
     def on_connection_closed(self):
         BaseReplicationStreamProtocol.on_connection_closed(self)
         self.streamer.lost_connection(self)
@@ -589,6 +596,11 @@ class AbstractReplicationClientHandler(metaclass=abc.ABCMeta):
         raise NotImplementedError()
 
     @abc.abstractmethod
+    async def on_remote_server_up(self, server: str):
+        """Called when get a new REMOTE_SERVER_UP command."""
+        raise NotImplementedError()
+
+    @abc.abstractmethod
     def get_streams_to_replicate(self):
         """Called when a new connection has been established and we need to
         subscribe to streams.
@@ -707,6 +719,9 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
     async def on_SYNC(self, cmd):
         self.handler.on_sync(cmd.data)
 
+    async def on_REMOTE_SERVER_UP(self, cmd: RemoteServerUpCommand):
+        self.handler.on_remote_server_up(cmd.data)
+
     def replicate(self, stream_name, token):
         """Send the subscription request to the server
         """
diff --git a/synapse/replication/tcp/resource.py b/synapse/replication/tcp/resource.py
index b1752e88cd..6ebf944f66 100644
--- a/synapse/replication/tcp/resource.py
+++ b/synapse/replication/tcp/resource.py
@@ -120,6 +120,7 @@ class ReplicationStreamer(object):
             self.federation_sender = hs.get_federation_sender()
 
         self.notifier.add_replication_callback(self.on_notifier_poke)
+        self.notifier.add_remote_server_up_callback(self.send_remote_server_up)
 
         # Keeps track of whether we are currently checking for updates
         self.is_looping = False
@@ -288,6 +289,14 @@ class ReplicationStreamer(object):
         )
         await self._server_notices_sender.on_user_ip(user_id)
 
+    @measure_func("repl.on_remote_server_up")
+    def on_remote_server_up(self, server: str):
+        self.notifier.notify_remote_server_up(server)
+
+    def send_remote_server_up(self, server: str):
+        for conn in self.connections:
+            conn.send_remote_server_up(server)
+
     def send_sync_to_all_connections(self, data):
         """Sends a SYNC command to all clients.