#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright 2015, 2016 OpenMarket Ltd
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#
import logging
import random
from types import TracebackType
from typing import TYPE_CHECKING, Any, Optional, Type
from synapse.api.errors import CodeMessageException
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.storage import DataStore
from synapse.types import StrCollection
from synapse.util import Clock
if TYPE_CHECKING:
from synapse.notifier import Notifier
from synapse.replication.tcp.handler import ReplicationCommandHandler
logger = logging.getLogger(__name__)
class NotRetryingDestination(Exception):
def __init__(self, retry_last_ts: int, retry_interval: int, destination: str):
"""Raised by the limiter (and federation client) to indicate that we are
are deliberately not attempting to contact a given server.
Args:
retry_last_ts: the unix ts in milliseconds of our last attempt
to contact the server. 0 indicates that the last attempt was
successful or that we've never actually attempted to connect.
retry_interval: the time in milliseconds to wait until the next
attempt.
destination: the domain in question
"""
msg = f"Not retrying server {destination} because we tried it recently retry_last_ts={retry_last_ts} and we won't check for another retry_interval={retry_interval}ms."
super().__init__(msg)
self.retry_last_ts = retry_last_ts
self.retry_interval = retry_interval
self.destination = destination
async def get_retry_limiter(
destination: str,
clock: Clock,
store: DataStore,
ignore_backoff: bool = False,
**kwargs: Any,
) -> "RetryDestinationLimiter":
"""For a given destination check if we have previously failed to
send a request there and are waiting before retrying the destination.
If we are not ready to retry the destination, this will raise a
NotRetryingDestination exception. Otherwise, will return a Context Manager
that will mark the destination as down if an exception is thrown (excluding
CodeMessageException with code < 500)
Args:
destination: name of homeserver
clock: timing source
store: datastore
ignore_backoff: true to ignore the historical backoff data and
try the request anyway. We will still reset the retry_interval on success.
Example usage:
try:
limiter = await get_retry_limiter(destination, clock, store)
with limiter:
response = await do_request()
except NotRetryingDestination:
# We aren't ready to retry that destination.
raise
"""
failure_ts = None
retry_last_ts, retry_interval = (0, 0)
retry_timings = await store.get_destination_retry_timings(destination)
if retry_timings:
failure_ts = retry_timings.failure_ts
retry_last_ts = retry_timings.retry_last_ts
retry_interval = retry_timings.retry_interval
now = int(clock.time_msec())
if not ignore_backoff and retry_last_ts + retry_interval > now:
raise NotRetryingDestination(
retry_last_ts=retry_last_ts,
retry_interval=retry_interval,
destination=destination,
)
# if we are ignoring the backoff data, we should also not increment the backoff
# when we get another failure - otherwise a server can very quickly reach the
# maximum backoff even though it might only have been down briefly
backoff_on_failure = not ignore_backoff
return RetryDestinationLimiter(
destination,
clock,
store,
failure_ts,
retry_interval,
backoff_on_failure=backoff_on_failure,
**kwargs,
)
async def filter_destinations_by_retry_limiter(
destinations: StrCollection,
clock: Clock,
store: DataStore,
retry_due_within_ms: int = 0,
) -> StrCollection:
"""Filter down the list of destinations to only those that will are either
alive or due for a retry (within `retry_due_within_ms`)
"""
if not destinations:
return destinations
retry_timings = await store.get_destination_retry_timings_batch(destinations)
now = int(clock.time_msec())
return [
destination
for destination, timings in retry_timings.items()
if timings is None
or timings.retry_last_ts + timings.retry_interval <= now + retry_due_within_ms
]
class RetryDestinationLimiter:
def __init__(
self,
destination: str,
clock: Clock,
store: DataStore,
failure_ts: Optional[int],
retry_interval: int,
backoff_on_404: bool = False,
backoff_on_failure: bool = True,
notifier: Optional["Notifier"] = None,
replication_client: Optional["ReplicationCommandHandler"] = None,
backoff_on_all_error_codes: bool = False,
):
"""Marks the destination as "down" if an exception is thrown in the
context, except for CodeMessageException with code < 500.
If no exception is raised, marks the destination as "up".
Args:
destination
clock
store
failure_ts: when this destination started failing (in ms since
the epoch), or zero if the last request was successful
retry_interval: The next retry interval taken from the
database in milliseconds, or zero if the last request was
successful.
backoff_on_404: Back off if we get a 404
backoff_on_failure: set to False if we should not increase the
retry interval on a failure.
notifier: A notifier used to mark servers as up.
replication_client A replication client used to mark servers as up.
backoff_on_all_error_codes: Whether we should back off on any
error code.
"""
self.clock = clock
self.store = store
self.destination = destination
self.failure_ts = failure_ts
self.retry_interval = retry_interval
self.backoff_on_404 = backoff_on_404
self.backoff_on_failure = backoff_on_failure
self.backoff_on_all_error_codes = backoff_on_all_error_codes
self.notifier = notifier
self.replication_client = replication_client
self.destination_min_retry_interval_ms = (
self.store.hs.config.federation.destination_min_retry_interval_ms
)
self.destination_retry_multiplier = (
self.store.hs.config.federation.destination_retry_multiplier
)
self.destination_max_retry_interval_ms = (
self.store.hs.config.federation.destination_max_retry_interval_ms
)
def __enter__(self) -> None:
pass
def __exit__(
self,
exc_type: Optional[Type[BaseException]],
exc_val: Optional[BaseException],
exc_tb: Optional[TracebackType],
) -> None:
success = exc_type is None
valid_err_code = False
if exc_type is None:
valid_err_code = True
elif not issubclass(exc_type, Exception):
# avoid treating exceptions which don't derive from Exception as
# failures; this is mostly so as not to catch defer._DefGen.
valid_err_code = True
elif isinstance(exc_val, CodeMessageException):
# Some error codes are perfectly fine for some APIs, whereas other
# APIs may expect to never received e.g. a 404. It's important to
# handle 404 as some remote servers will return a 404 when the HS
# has been decommissioned.
# If we get a 401, then we should probably back off since they
# won't accept our requests for at least a while.
# 429 is us being aggressively rate limited, so lets rate limit
# ourselves.
if self.backoff_on_all_error_codes:
valid_err_code = False
elif exc_val.code == 404 and self.backoff_on_404:
valid_err_code = False
elif exc_val.code in (401, 429):
valid_err_code = False
elif exc_val.code < 500:
valid_err_code = True
else:
valid_err_code = False
# Whether previous requests to the destination had been failing.
previously_failing = bool(self.failure_ts)
if success:
# We connected successfully.
if not self.retry_interval:
return
logger.debug(
"Connection to %s was successful; clearing backoff", self.destination
)
self.failure_ts = None
retry_last_ts = 0
self.retry_interval = 0
elif valid_err_code:
# We got a potentially valid error code back. We don't reset the
# timers though, as the other side might actually be down anyway
# (e.g. some deprovisioned servers will always return a 404 or 403,
# and we don't want to keep resetting the retry timers for them).
return
elif not self.backoff_on_failure:
return
else:
# We couldn't connect.
if self.retry_interval:
self.retry_interval = int(
self.retry_interval
* self.destination_retry_multiplier
* random.uniform(0.8, 1.4)
)
if self.retry_interval >= self.destination_max_retry_interval_ms:
self.retry_interval = self.destination_max_retry_interval_ms
else:
self.retry_interval = self.destination_min_retry_interval_ms
logger.info(
"Connection to %s was unsuccessful (%s(%s)); backoff now %i",
self.destination,
exc_type,
exc_val,
self.retry_interval,
)
retry_last_ts = int(self.clock.time_msec())
if self.failure_ts is None:
self.failure_ts = retry_last_ts
# Whether the current request to the destination had been failing.
currently_failing = bool(self.failure_ts)
async def store_retry_timings() -> None:
try:
await self.store.set_destination_retry_timings(
self.destination,
self.failure_ts,
retry_last_ts,
self.retry_interval,
)
# If the server was previously failing, but is no longer.
if previously_failing and not currently_failing:
if self.notifier:
# Inform the relevant places that the remote server is back up.
self.notifier.notify_remote_server_up(self.destination)
if self.replication_client:
# Inform other workers that the remote server is up.
self.replication_client.send_remote_server_up(self.destination)
except Exception:
logger.exception("Failed to store destination_retry_timings")
# we deliberately do this in the background.
run_as_background_process("store_retry_timings", store_retry_timings)