Add ability to shard the federation sender (#7798)

3 files changed, 132 insertions, 66 deletions

diff --git a/synapse/config/federation.py b/synapse/config/federation.py
new file mode 100644
index 0000000000..7782ab4c9d
--- /dev/null
+++ b/synapse/config/federation.py
@@ -0,0 +1,129 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from hashlib import sha256
+from typing import List, Optional
+
+import attr
+from netaddr import IPSet
+
+from ._base import Config, ConfigError
+
+
+@attr.s
+class ShardedFederationSendingConfig:
+    """Algorithm for choosing which federation sender instance is responsible
+    for which destionation host.
+    """
+
+    instances = attr.ib(type=List[str])
+
+    def should_send_to(self, instance_name: str, destination: str) -> bool:
+        """Whether this instance is responsible for sending transcations for
+        the given host.
+        """
+
+        # If multiple federation senders are not defined we always return true.
+        if not self.instances or len(self.instances) == 1:
+            return True
+
+        # We shard by taking the hash, modulo it by the number of federation
+        # senders and then checking whether this instance matches the instance
+        # at that index.
+        #
+        # (Technically this introduces some bias and is not entirely uniform, but
+        # since the hash is so large the bias is ridiculously small).
+        dest_hash = sha256(destination.encode("utf8")).digest()
+        dest_int = int.from_bytes(dest_hash, byteorder="little")
+        remainder = dest_int % (len(self.instances))
+        return self.instances[remainder] == instance_name
+
+
+class FederationConfig(Config):
+    section = "federation"
+
+    def read_config(self, config, **kwargs):
+        # Whether to send federation traffic out in this process. This only
+        # applies to some federation traffic, and so shouldn't be used to
+        # "disable" federation
+        self.send_federation = config.get("send_federation", True)
+
+        federation_sender_instances = config.get("federation_sender_instances") or []
+        self.federation_shard_config = ShardedFederationSendingConfig(
+            federation_sender_instances
+        )
+
+        # FIXME: federation_domain_whitelist needs sytests
+        self.federation_domain_whitelist = None  # type: Optional[dict]
+        federation_domain_whitelist = config.get("federation_domain_whitelist", None)
+
+        if federation_domain_whitelist is not None:
+            # turn the whitelist into a hash for speed of lookup
+            self.federation_domain_whitelist = {}
+
+            for domain in federation_domain_whitelist:
+                self.federation_domain_whitelist[domain] = True
+
+        self.federation_ip_range_blacklist = config.get(
+            "federation_ip_range_blacklist", []
+        )
+
+        # Attempt to create an IPSet from the given ranges
+        try:
+            self.federation_ip_range_blacklist = IPSet(
+                self.federation_ip_range_blacklist
+            )
+
+            # Always blacklist 0.0.0.0, ::
+            self.federation_ip_range_blacklist.update(["0.0.0.0", "::"])
+        except Exception as e:
+            raise ConfigError(
+                "Invalid range(s) provided in federation_ip_range_blacklist: %s" % e
+            )
+
+    def generate_config_section(self, config_dir_path, server_name, **kwargs):
+        return """\
+        # Restrict federation to the following whitelist of domains.
+        # N.B. we recommend also firewalling your federation listener to limit
+        # inbound federation traffic as early as possible, rather than relying
+        # purely on this application-layer restriction.  If not specified, the
+        # default is to whitelist everything.
+        #
+        #federation_domain_whitelist:
+        #  - lon.example.com
+        #  - nyc.example.com
+        #  - syd.example.com
+
+        # Prevent federation requests from being sent to the following
+        # blacklist IP address CIDR ranges. If this option is not specified, or
+        # specified with an empty list, no ip range blacklist will be enforced.
+        #
+        # As of Synapse v1.4.0 this option also affects any outbound requests to identity
+        # servers provided by user input.
+        #
+        # (0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
+        # listed here, since they correspond to unroutable addresses.)
+        #
+        federation_ip_range_blacklist:
+          - '127.0.0.0/8'
+          - '10.0.0.0/8'
+          - '172.16.0.0/12'
+          - '192.168.0.0/16'
+          - '100.64.0.0/10'
+          - '169.254.0.0/16'
+          - '::1/128'
+          - 'fe80::/64'
+          - 'fc00::/7'
+        """
diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index 264c274c52..8e93d31394 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -23,6 +23,7 @@ from .cas import CasConfig
 from .consent_config import ConsentConfig
 from .database import DatabaseConfig
 from .emailconfig import EmailConfig
+from .federation import FederationConfig
 from .groups import GroupsConfig
 from .jwt_config import JWTConfig
 from .key import KeyConfig
@@ -57,6 +58,7 @@ class HomeServerConfig(RootConfig):
     config_classes = [
         ServerConfig,
         TlsConfig,
+        FederationConfig,
         CacheConfig,
         DatabaseConfig,
         LoggingConfig,
@@ -90,4 +92,5 @@ class HomeServerConfig(RootConfig):
         ThirdPartyRulesConfig,
         TracerConfig,
         RedisConfig,
+        FederationConfig,
     ]
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 8204664883..b6afa642ca 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -23,7 +23,6 @@ from typing import Any, Dict, Iterable, List, Optional
 
 import attr
 import yaml
-from netaddr import IPSet
 
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.http.endpoint import parse_and_validate_server_name
@@ -136,11 +135,6 @@ class ServerConfig(Config):
         self.use_frozen_dicts = config.get("use_frozen_dicts", False)
         self.public_baseurl = config.get("public_baseurl")
 
-        # Whether to send federation traffic out in this process. This only
-        # applies to some federation traffic, and so shouldn't be used to
-        # "disable" federation
-        self.send_federation = config.get("send_federation", True)
-
         # Whether to enable user presence.
         self.use_presence = config.get("use_presence", True)
 
@@ -263,34 +257,6 @@ class ServerConfig(Config):
         # due to resource constraints
         self.admin_contact = config.get("admin_contact", None)
 
-        # FIXME: federation_domain_whitelist needs sytests
-        self.federation_domain_whitelist = None  # type: Optional[dict]
-        federation_domain_whitelist = config.get("federation_domain_whitelist", None)
-
-        if federation_domain_whitelist is not None:
-            # turn the whitelist into a hash for speed of lookup
-            self.federation_domain_whitelist = {}
-
-            for domain in federation_domain_whitelist:
-                self.federation_domain_whitelist[domain] = True
-
-        self.federation_ip_range_blacklist = config.get(
-            "federation_ip_range_blacklist", []
-        )
-
-        # Attempt to create an IPSet from the given ranges
-        try:
-            self.federation_ip_range_blacklist = IPSet(
-                self.federation_ip_range_blacklist
-            )
-
-            # Always blacklist 0.0.0.0, ::
-            self.federation_ip_range_blacklist.update(["0.0.0.0", "::"])
-        except Exception as e:
-            raise ConfigError(
-                "Invalid range(s) provided in federation_ip_range_blacklist: %s" % e
-            )
-
         if self.public_baseurl is not None:
             if self.public_baseurl[-1] != "/":
                 self.public_baseurl += "/"
@@ -743,38 +709,6 @@ class ServerConfig(Config):
         #
         #enable_search: false
 
-        # Restrict federation to the following whitelist of domains.
-        # N.B. we recommend also firewalling your federation listener to limit
-        # inbound federation traffic as early as possible, rather than relying
-        # purely on this application-layer restriction.  If not specified, the
-        # default is to whitelist everything.
-        #
-        #federation_domain_whitelist:
-        #  - lon.example.com
-        #  - nyc.example.com
-        #  - syd.example.com
-
-        # Prevent federation requests from being sent to the following
-        # blacklist IP address CIDR ranges. If this option is not specified, or
-        # specified with an empty list, no ip range blacklist will be enforced.
-        #
-        # As of Synapse v1.4.0 this option also affects any outbound requests to identity
-        # servers provided by user input.
-        #
-        # (0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
-        # listed here, since they correspond to unroutable addresses.)
-        #
-        federation_ip_range_blacklist:
-          - '127.0.0.0/8'
-          - '10.0.0.0/8'
-          - '172.16.0.0/12'
-          - '192.168.0.0/16'
-          - '100.64.0.0/10'
-          - '169.254.0.0/16'
-          - '::1/128'
-          - 'fe80::/64'
-          - 'fc00::/7'
-
         # List of ports that Synapse should listen on, their purpose and their
         # configuration.
         #