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![Erik Johnston](/assets/img/avatar_default.png)
For direct TCP connections we need the master to relay REMOTE_SERVER_UP commands to the other connections so that all instances get notified about it. The old implementation just relayed to all connections, assuming that sending back to the original sender of the command was safe. This is not true for redis, where commands sent get echoed back to the sender, which was causing master to effectively infinite loop sending and then re-receiving REMOTE_SERVER_UP commands that it sent. The fix is to ensure that we only relay to *other* connections and not to the connection we received the notification from. Fixes #7334.
194 lines
6.4 KiB
Python
194 lines
6.4 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2020 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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from typing import TYPE_CHECKING
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import txredisapi
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from synapse.logging.context import PreserveLoggingContext
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from synapse.metrics.background_process_metrics import run_as_background_process
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from synapse.replication.tcp.commands import (
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Command,
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ReplicateCommand,
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parse_command_from_line,
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)
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from synapse.replication.tcp.protocol import (
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AbstractConnection,
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tcp_inbound_commands_counter,
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tcp_outbound_commands_counter,
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)
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if TYPE_CHECKING:
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from synapse.replication.tcp.handler import ReplicationCommandHandler
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from synapse.server import HomeServer
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logger = logging.getLogger(__name__)
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class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
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"""Connection to redis subscribed to replication stream.
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Parses incoming messages from redis into replication commands, and passes
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them to `ReplicationCommandHandler`
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Due to the vagaries of `txredisapi` we don't want to have a custom
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constructor, so instead we expect the defined attributes below to be set
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immediately after initialisation.
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Attributes:
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handler: The command handler to handle incoming commands.
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stream_name: The *redis* stream name to subscribe to (not anything to
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do with Synapse replication streams).
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outbound_redis_connection: The connection to redis to use to send
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commands.
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"""
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handler = None # type: ReplicationCommandHandler
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stream_name = None # type: str
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outbound_redis_connection = None # type: txredisapi.RedisProtocol
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def connectionMade(self):
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logger.info("Connected to redis instance")
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self.subscribe(self.stream_name)
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self.send_command(ReplicateCommand())
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self.handler.new_connection(self)
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def messageReceived(self, pattern: str, channel: str, message: str):
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"""Received a message from redis.
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"""
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if message.strip() == "":
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# Ignore blank lines
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return
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try:
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cmd = parse_command_from_line(message)
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except Exception:
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logger.exception(
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"[%s] failed to parse line: %r", message,
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)
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return
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# We use "redis" as the name here as we don't have 1:1 connections to
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# remote instances.
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tcp_inbound_commands_counter.labels(cmd.NAME, "redis").inc()
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# Now lets try and call on_<CMD_NAME> function
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run_as_background_process(
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"replication-" + cmd.get_logcontext_id(), self.handle_command, cmd
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)
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async def handle_command(self, cmd: Command):
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"""Handle a command we have received over the replication stream.
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By default delegates to on_<COMMAND>, which should return an awaitable.
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Args:
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cmd: received command
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"""
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handled = False
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# First call any command handlers on this instance. These are for redis
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# specific handling.
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cmd_func = getattr(self, "on_%s" % (cmd.NAME,), None)
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if cmd_func:
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await cmd_func(cmd)
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handled = True
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# Then call out to the handler.
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cmd_func = getattr(self.handler, "on_%s" % (cmd.NAME,), None)
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if cmd_func:
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await cmd_func(self, cmd)
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handled = True
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if not handled:
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logger.warning("Unhandled command: %r", cmd)
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def connectionLost(self, reason):
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logger.info("Lost connection to redis instance")
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self.handler.lost_connection(self)
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def send_command(self, cmd: Command):
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"""Send a command if connection has been established.
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Args:
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cmd (Command)
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"""
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string = "%s %s" % (cmd.NAME, cmd.to_line())
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if "\n" in string:
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raise Exception("Unexpected newline in command: %r", string)
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encoded_string = string.encode("utf-8")
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# We use "redis" as the name here as we don't have 1:1 connections to
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# remote instances.
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tcp_outbound_commands_counter.labels(cmd.NAME, "redis").inc()
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async def _send():
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with PreserveLoggingContext():
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# Note that we use the other connection as we can't send
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# commands using the subscription connection.
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await self.outbound_redis_connection.publish(
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self.stream_name, encoded_string
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)
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run_as_background_process("send-cmd", _send)
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class RedisDirectTcpReplicationClientFactory(txredisapi.SubscriberFactory):
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"""This is a reconnecting factory that connects to redis and immediately
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subscribes to a stream.
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Args:
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hs
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outbound_redis_connection: A connection to redis that will be used to
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send outbound commands (this is seperate to the redis connection
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used to subscribe).
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"""
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maxDelay = 5
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continueTrying = True
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protocol = RedisSubscriber
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def __init__(
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self, hs: "HomeServer", outbound_redis_connection: txredisapi.RedisProtocol
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):
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super().__init__()
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# This sets the password on the RedisFactory base class (as
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# SubscriberFactory constructor doesn't pass it through).
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self.password = hs.config.redis.redis_password
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self.handler = hs.get_tcp_replication()
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self.stream_name = hs.hostname
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self.outbound_redis_connection = outbound_redis_connection
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def buildProtocol(self, addr):
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p = super().buildProtocol(addr) # type: RedisSubscriber
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# We do this here rather than add to the constructor of `RedisSubcriber`
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# as to do so would involve overriding `buildProtocol` entirely, however
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# the base method does some other things than just instantiating the
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# protocol.
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p.handler = self.handler
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p.outbound_redis_connection = self.outbound_redis_connection
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p.stream_name = self.stream_name
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return p
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