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- # Copyright 2015, 2016 OpenMarket Ltd
- #
- # 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.
- import logging
- import random
- import synapse.logging.context
- from synapse.api.errors import CodeMessageException
- logger = logging.getLogger(__name__)
- # the initial backoff, after the first transaction fails
- MIN_RETRY_INTERVAL = 10 * 60 * 1000
- # how much we multiply the backoff by after each subsequent fail
- RETRY_MULTIPLIER = 5
- # a cap on the backoff. (Essentially none)
- MAX_RETRY_INTERVAL = 2 ** 62
- class NotRetryingDestination(Exception):
- def __init__(self, retry_last_ts, retry_interval, destination):
- """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 (int): 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 (int): the time in milliseconds to wait until the next
- attempt.
- destination (str): the domain in question
- """
- msg = "Not retrying server %s." % (destination,)
- super().__init__(msg)
- self.retry_last_ts = retry_last_ts
- self.retry_interval = retry_interval
- self.destination = destination
- async def get_retry_limiter(destination, clock, store, ignore_backoff=False, **kwargs):
- """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 (str): name of homeserver
- clock (synapse.util.clock): timing source
- store (synapse.storage.transactions.TransactionStore): datastore
- ignore_backoff (bool): 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,
- )
- class RetryDestinationLimiter:
- def __init__(
- self,
- destination,
- clock,
- store,
- failure_ts,
- retry_interval,
- backoff_on_404=False,
- backoff_on_failure=True,
- ):
- """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 (str)
- clock (Clock)
- store (DataStore)
- failure_ts (int|None): when this destination started failing (in ms since
- the epoch), or zero if the last request was successful
- retry_interval (int): The next retry interval taken from the
- database in milliseconds, or zero if the last request was
- successful.
- backoff_on_404 (bool): Back off if we get a 404
- backoff_on_failure (bool): set to False if we should not increase the
- retry interval on a failure.
- """
- 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
- def __enter__(self):
- pass
- def __exit__(self, exc_type, exc_val, exc_tb):
- 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 issubclass(exc_type, 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 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
- if valid_err_code:
- # 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 not self.backoff_on_failure:
- return
- else:
- # We couldn't connect.
- if self.retry_interval:
- self.retry_interval = int(
- self.retry_interval * RETRY_MULTIPLIER * random.uniform(0.8, 1.4)
- )
- if self.retry_interval >= MAX_RETRY_INTERVAL:
- self.retry_interval = MAX_RETRY_INTERVAL
- else:
- self.retry_interval = MIN_RETRY_INTERVAL
- 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
- async def store_retry_timings():
- try:
- await self.store.set_destination_retry_timings(
- self.destination,
- self.failure_ts,
- retry_last_ts,
- self.retry_interval,
- )
- except Exception:
- logger.exception("Failed to store destination_retry_timings")
- # we deliberately do this in the background.
- synapse.logging.context.run_in_background(store_retry_timings)
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