# -*- coding: utf-8 -*- # 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_interval = ( retry_timings["retry_last_ts"], 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)