diff --git a/synapse/config/_base.py b/synapse/config/_base.py
index 1391e5fc43..fd137853b1 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -19,9 +19,11 @@ import argparse
import errno
import os
from collections import OrderedDict
+from hashlib import sha256
from textwrap import dedent
-from typing import Any, MutableMapping, Optional
+from typing import Any, List, MutableMapping, Optional
+import attr
import yaml
@@ -717,4 +719,36 @@ def find_config_files(search_paths):
return config_files
-__all__ = ["Config", "RootConfig"]
+@attr.s
+class ShardedWorkerHandlingConfig:
+ """Algorithm for choosing which instance is responsible for handling some
+ sharded work.
+
+ For example, the federation senders use this to determine which instances
+ handles sending stuff to a given destination (which is used as the `key`
+ below).
+ """
+
+ instances = attr.ib(type=List[str])
+
+ def should_handle(self, instance_name: str, key: str) -> bool:
+ """Whether this instance is responsible for handling the given key.
+ """
+
+ # If multiple instances 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 instances 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(key.encode("utf8")).digest()
+ dest_int = int.from_bytes(dest_hash, byteorder="little")
+ remainder = dest_int % (len(self.instances))
+ return self.instances[remainder] == instance_name
+
+
+__all__ = ["Config", "RootConfig", "ShardedWorkerHandlingConfig"]
|
